The Hot Tub in the Four Courts? An Analysis of Concurrent Expert Evidence in the Irish Legal System

Concurrent Expert Evidence, a procedural innovation colloquially known as “hot-tubbing,” represents one of the most significant shifts in modern civil litigation, challenging the centuries-old adversarial tradition of handling expert testimony. Originating in Australia and now adopted across the common law world, this method brings experts together to testify concurrently, engaging in a judge-led dialogue aimed at enhancing clarity, efficiency, and the court’s truth-finding function. This paper provides an in-depth analysis of this global procedure through an Irish lens, examining its formal introduction into the Irish legal system as a “debate amongst experts.” It contrasts the cautious, limited application in Ireland with the more established models abroad, exploring the judicial appetite, cultural barriers, and practical implications of seating experts together in a metaphorical hot tub within the historic confines of the Four Courts.

Part I: Introduction to Concurrent Expert Evidence

1.1. Defining the ‘Hot Tub’: From Australian Innovation to Global Procedure

In the landscape of civil procedure reform, few innovations have generated as much discussion, debate, and curiosity as Concurrent Expert Evidence (CCE), a technique colloquially and almost universally known as “hot-tubbing”.¹ At its core, CCE is a method for receiving evidence where expert witnesses from the same or similar disciplines are sworn in and testify at the same time, rather than in the traditional sequential manner.¹ This represents a significant departure from the conventional adversarial process, where each party’s expert is called, gives their evidence-in-chief, is cross-examined by the opposing side, and then potentially re-examined, often with days or even weeks separating their respective testimonies.

The procedure originated and was pioneered in Australia, where it has been in use for several decades and is now a mature and entrenched feature of the court system, particularly in complex commercial and technical disputes.⁵ From its Australian origins, the practice has migrated across the common law world, finding favour in various forms in the United Kingdom, Canada, and the United States federal courts, as well as in international arbitration and specialised tribunals such as those dealing with European competition law.⁵ The term “hot-tubbing” itself, while informal, aptly captures the essence of the process: a group of experts immersed together in the technical issues of the case, engaging in a direct and focused dialogue under the guidance of the court.

The introduction of CCE is not merely a procedural adjustment; it signifies a deeper philosophical shift in how the legal system approaches the truth-finding function of expert evidence. The traditional adversarial system, with its emphasis on party-led examination and cross-examination, can often frame expert evidence as another battleground in the litigation war. CCE seeks to re-cast the role of the expert, moving them away from being a “hired gun” for one side and towards their proper function as an independent assistant to the court. This is achieved by changing the dynamic of the hearing itself. Instead of a series of isolated monologues punctuated by adversarial questioning, CCE creates a structured, multi-party conversation. The primary interlocutors are no longer just the lawyer and the witness, but the experts themselves and, crucially, the judge. This shift places the judge in a more proactive, inquisitorial role, empowering them to moderate the discussion, probe areas of disagreement, and seek direct clarification on complex points.⁷ This transformation of the judge from a passive umpire to an active chairperson is fundamental to the CCE process and represents its most significant departure from conventional trial practice.

1.2. Core Aims: The Pursuit of Efficiency, Clarity, and Truth

The rationale underpinning the development and adoption of CCE is multi-faceted, but its core objectives can be distilled into the pursuit of greater efficiency, enhanced judicial comprehension, and a more reliable path to the substantive truth of the technical matters in dispute. Proponents argue that the traditional method of hearing expert evidence is often inefficient, costly, and ill-suited to resolving complex technical disagreements.⁹ The sequential nature of testimony can lead to a situation aptly described as “two ships passing in the night,” where opposing expert opinions are presented in isolation, making it exceedingly difficult for the judge to conduct a direct, real-time comparison of their methodologies, assumptions, and conclusions.¹ The true nature of the dispute between the experts may only become apparent long after the evidence has been heard, during the review of transcripts and closing submissions, a process that is both cumbersome and prone to misunderstanding.⁹

CCE aims to remedy these deficiencies by transforming the evidentiary process from a confrontational battle into a more cooperative and collegiate enterprise geared towards genuine inquiry.⁹ The primary goal is to assist the court in understanding the evidence. By having experts discuss the issues with each other in the judge’s presence, the process allows for immediate clarification of technical terms, direct comparison of conflicting theories, and the identification of the precise reasons for disagreement—be it a different factual assumption, a different analytical methodology, or a fundamental divergence in professional opinion.⁵ This structured dialogue is intended to cut through the “window dressing” and legalistic framing of traditional cross-examination, focusing instead on the substantive scientific or technical issues.⁹

Ultimately, the overarching purpose of CCE is to better serve the objectives of justice by making the resolution of disputes, in the words of the Australian procedural ideal, “just, quick and cheap”.¹¹ By improving the quality and comprehensibility of expert evidence, the process aims to enable the judge to make a more informed and accurate decision. By narrowing the issues in dispute before and during the hearing, it seeks to reduce the time and expense of litigation, not only by shortening the trial itself but also by providing the parties with a clearer picture of their case’s strengths and weaknesses, thereby facilitating more realistic and timely settlements.¹

1.3. The Mechanics of CCE: A Procedural Overview

While the application of CCE is known for its flexibility, with the trial judge retaining discretion over the precise format, a typical model has emerged from practice in jurisdictions like Australia.⁵ This model generally involves three distinct stages, each designed to progressively refine the issues and focus the hearing on the areas of genuine disagreement.

Stage 1: The Pre-Trial Expert Conference (‘Conclave’)

The process usually begins after the experts for each party have prepared and exchanged their individual written reports. The court then directs the experts of like disciplines to meet privately, in a “conclave,” without the parties or their legal representatives present.5 The purpose of this meeting is for the experts to engage in a robust, professional discussion to identify the precise areas on which they agree and, more importantly, the areas where their opinions diverge. This stage is critical for issue-narrowing. Experts are often surprised to find that their areas of genuine disagreement are far more limited than the adversarial framing of the litigation might suggest.5 However, this stage is not without risk for the parties. The discussions are not typically privileged, and an ill-prepared or unwary expert could make a damaging concession that has significant ramifications for their party’s case.5 Therefore, thorough preparation of the expert by their instructing solicitors is essential before the conclave begins.

Stage 2: The Joint Report

The key output of the conclave is a single joint report, or joint statement, signed by all participating experts.5 This document, often structured around a list of questions or topics defined by the judge, sets out with clarity the matters upon which the experts have reached a consensus and the matters that remain in dispute. For each point of disagreement, the report requires the experts to provide a concise summary of their differing opinions and the reasons for their disagreement.5 This joint report becomes an invaluable roadmap for the court and the parties. It distils potentially thousands of pages of technical reports into a manageable summary of the core issues, ensuring that the subsequent court hearing is focused, efficient, and directed only at the matters that require judicial determination.5 This report can also be a powerful catalyst for settlement, as it provides an objective and unvarnished assessment of the expert contest.5

Stage 3: Concurrent Testimony in the ‘Hot Tub’

The final stage is the concurrent hearing itself. The experts are sworn in together and typically sit together in the witness box or at a table before the judge.1 The judge, using the joint report as an agenda, chairs a structured discussion.7 The judge will typically initiate the process by asking each expert in turn to summarise their view on the first issue of disagreement. The experts are then encouraged to comment on each other’s opinions and to ask questions of each other directly.1 This peer-to-peer dialogue is the hallmark of hot-tubbing. After the judge-led discussion on each topic is complete, the parties’ legal counsel are given the opportunity to ask further questions. This questioning is not a traditional cross-examination but is more focused on clarifying the evidence that has emerged during the experts’ discussion and testing the opinions that have been expressed.1 The entire process is designed to be a “co-operative endeavour” to educate the court, rather than an adversarial contest.7

Part II: The Traditional Landscape of Expert Evidence in Ireland

2.1. The Expert’s Overriding Duty: A Pillar of the Irish System

Before examining Ireland’s specific engagement with CCE, it is essential to understand the foundational principles that govern the role of the expert witness within the Irish legal system. The cornerstone of this framework is the unequivocal principle that an expert witness’s primary and overriding duty is to the court.¹³ This duty of independence and objectivity supersedes any obligation, perceived or real, to the party who has instructed them and is paying their fee.¹⁵

This principle, long established in common law and famously articulated in the English High Court decision of National Justice Compania Naviera SA v Prudential Assurance Co Ltd (The Ikarian Reefer) 2 Lloyd’s Rep 68, has been unequivocally adopted and reinforced within Irish jurisprudence.¹³ More significantly, what was once a principle of case law has now been formally codified in the

Rules of the Superior Courts. Specifically, Order 39, Rule 57(1), introduced in 2016, states: “It is the duty of an expert to assist the court as to matters within his or her field of expertise. This duty overrides any obligation to any party paying the fee of the expert”.¹³

To ensure this duty is not merely an abstract concept, the rules further mandate that an expert’s report must contain an explicit statement acknowledging this duty.¹⁵ The core components of this duty, as elaborated in case law and legal guidance, require the expert to:

• Provide independent, objective, and unbiased opinion confined strictly to matters within their expertise.¹³
• Never assume the role of an advocate for the party instructing them.¹³
• State all facts and assumptions upon which their opinion is based, and to consider all material facts, including those that might detract from their concluded opinion.¹⁴
• Cooperate with other experts when required, with the aim of narrowing the issues in dispute.¹³
• Communicate any change of mind on a material issue to the parties and the court without delay.¹³

This robust framework underscores that the expert’s role in an Irish courtroom is that of an impartial educator, whose purpose is to provide the judge with the necessary specialist knowledge to enable the court to reach its own independent conclusion on the facts.¹⁵

2.2. Judicial Scrutiny and the ‘Hired Gun’: Reinforcing Independence

The Irish judiciary has, particularly in recent years, demonstrated an increasing resolve to rigorously enforce the expert’s duty of independence and to penalise those who fail to adhere to it. The perception of an expert as a “hired gun,” whose opinion is tailored to suit the needs of their client’s case, is one that the courts are actively seeking to eradicate.¹³

A landmark decision in this regard is the Court of Appeal judgment in Duffy v McGee IECA 254. In this case, the court delivered a powerful rebuke to an expert witness whose evidence was found to have crossed the line from objective opinion into advocacy. Mr Justice Noonan, in his judgment, forcefully reiterated the principles of expert conduct, stating that “The overriding duty of the expert is owed to the court and includes the duty to provide an objective opinion. Objectivity, by definition, requires that one has regard to both sides of the case”.¹⁴ The court identified several “red flags” in the expert’s evidence, including expressing views on legal doctrines outside his expertise, making categorical statements on disputed facts of which he had no independent knowledge, and accusing the opposing parties of misrepresentation.¹⁵

The decision in Duffy v McGee, and other similar judicial pronouncements, signals a clear judicial intolerance for partisan expert evidence.¹⁶ Courts have shown a readiness to attach little or no weight to the evidence of experts who are perceived to have fundamentally misunderstood their role and acted as a “mouthpiece” for their client.¹⁶ This has profound consequences, not only for the expert’s credibility but for the party’s entire case. Furthermore, the courts have highlighted the important responsibility of the legal practitioners instructing the expert to ensure their witness understands and complies with their duties, with the potential for wasted costs orders to be made against solicitors who fail in this regard.¹⁴ This judicial activism serves as a stark warning to both experts and their instructing lawyers that the duty to the court is paramount and its breach will not be tolerated.

2.3. The Inherent Challenges of the Adversarial Approach

Despite the strong substantive principles governing expert duties in Ireland, the traditional procedural framework for hearing that evidence presents inherent challenges. The conventional adversarial method, involving the sequential examination and cross-examination of each party’s expert, creates a structural tension with the expert’s duty of independence. While the law demands that the expert be a neutral assistant to the court, the procedure itself places them squarely within an adversarial context, instructed and presented by one side to be attacked by the other. This very structure can unconsciously or consciously encourage experts to view themselves as part of a “team” and to assume the role of an advocate, a tendency noted by the judiciary itself.¹⁶

This procedural model is often criticised for its inefficiency and its limited effectiveness in clarifying complex technical disputes. The process of hearing from one expert, followed days later by another, makes it difficult for the judge to directly compare their evidence and reconcile their differing views.⁹ This disconnected presentation of testimony has been described as being like “two ships passing in the night”.¹ A meaningful opportunity for a holistic analysis of the expert evidence often only arises after the trial has concluded, forcing the judge to undertake a cumbersome reconciliation of written transcripts.⁹

Furthermore, traditional cross-examination, while a powerful tool for testing factual evidence, may not be the most effective method for testing complex scientific or technical opinions. A lawyer’s questioning, however skilled, can become overly legalistic and may fail to engage with the core scientific disagreements between the experts. The process can be unsettling for the expert and risks sidelining the critical technical issues in favour of adversarial point-scoring.⁹ It is this context—the tension between the expert’s duty and the adversarial procedure, coupled with the inefficiencies and limitations of the traditional method—that provides the compelling rationale for the Irish legal system to consider and, in a limited fashion, adopt procedural reforms like Concurrent Expert Evidence. The introduction of mechanisms that facilitate direct dialogue between experts is a structural attempt to resolve this tension, aiming to create a procedure that better aligns with the expert’s fundamental duty to the court.

Part III: Ireland’s Tentative Step: The “Debate Amongst Experts”

3.1. The Genesis of Reform: S.I. No. 254/2016

The most significant development towards the adoption of a CCE-like procedure in Ireland came with the introduction of the Rules of the Superior Courts (Conduct of Trials) 2016 (S.I. No. 254 of 2016).²² These rules, which came into effect in late 2016, introduced a raft of new case management powers for High Court judges, primarily aimed at enhancing the efficiency and expediency of civil litigation, particularly in complex and lengthy cases.²⁴ While the rules covered various aspects of trial management, including time management and the exchange of witness statements, their most novel provisions related to the handling of expert evidence.²³ It is within this statutory instrument that Ireland took its first formal, albeit cautious, step towards embracing the principles of hot-tubbing.

3.2. Dissecting the Procedure: Joint Meetings and the “Debate”

S.I. No. 254 of 2016 introduced a new framework for managing expert evidence that closely mirrors the key components of the CCE process seen in other jurisdictions. The procedure is effectively a two-stage process, giving the judge discretionary power to direct a more collaborative approach to expert testimony.

Stage 1: The Joint Report

The rules empower the court to order experts from opposing sides to meet privately, “without the presence of any party or any legal representative of any party,” to discuss their proposed evidence.12 This provision directly reflects the “conclave” model. Following this private meeting, the experts are required to draw up and sign a “joint report.” This report must identify the evidence that is agreed between them and, crucially, the evidence that is not agreed.12 The purpose of this stage is to narrow the issues in dispute before the trial begins, thereby reducing the quantity of material that needs to be examined in court and focusing the hearing on the areas of genuine contention.22

Stage 2: The “Debate Amongst Experts”

The second and more innovative procedure introduced by the rules is what is explicitly termed a “debate amongst experts”.22 This mechanism is widely recognised by legal commentators as the Irish equivalent of “hot-tubbing”.22 The procedure involves the relevant experts being sworn in together, providing a summary of their opinions on the matters where they are not agreed, and then, if directed by the court, engaging in a debate with each other on these points of disagreement.22 During this debate, the judge acts as an “umpire” or moderator.22 Only after this debate has concluded may the court permit examination and cross-examination of the experts by the parties’ legal representatives on the matters discussed.24

3.3. Scope and Application

A critical feature of the Irish approach is the limited scope of these new powers. The provisions for joint reports and the “debate amongst experts” are not available in all civil proceedings. Their application is specifically confined to cases being heard in certain managed lists of the High Court, namely the Commercial List, the Competition List, Chancery actions, and other designated non-jury actions.²³

Significantly, the rules explicitly state that these particular provisions do not apply to personal injuries actions.²² This exclusion is highly consequential, as personal injury litigation constitutes a very large proportion of the civil caseload in the Irish High Court. This deliberate legislative choice to circumscribe the use of the “debate amongst experts” reveals a cautious, incremental approach to procedural reform. The Oireachtas and the Rules Committee have evidently chosen to introduce this novel technique in a controlled environment, limiting it to complex commercial disputes where the issues are often highly technical and the parties are typically well-resourced corporate entities. This suggests a “test the waters” strategy, allowing the judiciary and legal profession to gain experience with the procedure in a specific context before any consideration is given to its wider application. The result is a hybrid system where the traditional adversarial approach remains the default for the majority of civil cases, while a more inquisitorial, collaborative model is available as a discretionary tool in the most complex commercial matters. This measured implementation, combined with a scarcity of reported cases where the procedure has been invoked, indicates that while the mechanism exists on paper, it has yet to become a routine feature of Irish litigation.²²

Procedural Comparison of Expert Evidence Models

To provide a clear understanding of the changes introduced by S.I. No. 254 of 2016, the following table contrasts the traditional adversarial model of expert evidence with the new “Debate Amongst Experts” model.

Procedural Stage	Traditional Adversarial Model	“Debate Amongst Experts” Model (per S.I. 254/2016)
Expert Instruction	Parties independently instruct their own experts.	Parties independently instruct their own experts. The court may also order the appointment of a single joint expert.24
Report Preparation	Experts prepare individual reports based on instructions from their party’s legal team.	Experts prepare individual reports. These are exchanged between the parties.22
Pre-Trial Interaction	No formal requirement for opposing experts to meet or communicate.	Court may direct experts to meet privately (without lawyers) to discuss their evidence.12
Pre-Trial Output	Exchange of individual expert reports.30	Following their private meeting, experts must prepare a single “joint report” identifying areas of agreement and disagreement.12
In-Court Testimony (Examination-in-Chief)	Each expert is called sequentially by their party’s counsel to give oral evidence-in-chief, typically based on their report.	Experts are sworn in together. They provide a summary of their opinions on the points of disagreement identified in the joint report.22
In-Court Testimony (Testing of Evidence)	Each expert is cross-examined sequentially by the opposing party’s counsel. This is followed by potential re-examination.	Experts engage in a “debate” on the points of disagreement, with the judge acting as an “umpire.” Experts may question each other directly.22 Examination by counsel may be permitted	after this debate.24
Role of Judge	Primarily a passive role, observing the examination and cross-examination conducted by counsel.	An active, inquisitorial role. The judge chairs and moderates the “debate,” acting as an “umpire” and directing the discussion.22
Role of Counsel	Central role. Counsel controls the questioning and presentation of their expert’s evidence through examination-in-chief and cross-examination.	A diminished role during the core evidence-giving phase. Counsel’s opportunity to question is secondary to the judge-led debate between the experts.28

Part IV: Law Reform and Judicial Appetite for CCE in Ireland

4.1. The Law Reform Commission’s View: A Considered Omission

The journey of procedural reform in Ireland is often guided by the work of the Law Reform Commission (LRC), an independent statutory body tasked with reviewing and recommending changes to modernise Irish law.³¹ The LRC’s engagement with the topic of expert evidence provides a crucial insight into the official thinking on CCE.

In its comprehensive 2008 Consultation Paper on Expert Evidence (LRC CP 52-2008), the Commission dedicated significant analysis to alternative models for handling expert testimony, including a detailed discussion of CCE, which it referred to as the “panel of experts” or “hot tub” model.³¹ The paper accurately described the procedure as pioneered by the Australian Competition Tribunal, outlining the process of experts debating issues amongst themselves and being questioned by the tribunal before counsel’s involvement.³¹ It diligently canvassed the arguments for and against the model, noting its potential to reduce adversarial bias, costs, and delays, while also acknowledging criticisms regarding the potential for a more articulate expert to dominate and concerns about its compatibility with the right to present one’s own evidence.³¹

However, what is most telling is what happened next. Despite this thorough consideration in 2008, when the LRC published its final 2016 Report on Consolidation and Reform of Aspects of the Law of Evidence, it made no recommendation for the legislative adoption of CCE.³³ The final report, and the accompanying draft Evidence (Consolidation and Reform) Bill, focused instead on other critical areas of expert evidence reform. The key recommendations centred on placing the duties of an expert witness on a statutory footing, proposing a legislative definition of an “expert,” and, significantly, recommending the abolition of the traditional immunity from suit for expert witnesses.¹⁴

This omission of CCE from the final legislative proposals is a considered and significant act. It suggests that in 2016, the LRC, after extensive consultation, concluded that either the case for mandating CCE through primary legislation was not sufficiently compelling, or that such a procedural matter was better left to the more flexible and discretionary realm of the Rules of the Superior Courts. The LRC’s focus remained firmly on the status, duties, and accountability of the expert, rather than on the specific method by which their evidence should be presented in court.

4.2. Judicial Commentary and Uptake: A Quiet Evolution

The introduction of the “debate amongst experts” via S.I. No. 254/2016 created the potential for a significant shift in trial practice. However, an examination of the years since its introduction reveals a quiet and slow evolution rather than a rapid embrace of the new procedure. A notable feature of the Irish legal landscape is the scarcity of reported case law in which the procedure has been ordered, utilised, or judicially analysed.²² One legal commentary from 2017 noted that there was “very little Irish case law on this point,” and another observed that the procedure had been “rarely used” even in the Commercial Court, the very forum for which it was designed.²²

This limited uptake suggests a degree of caution or perhaps inertia within the legal profession and the judiciary. The focus of recent high-profile judicial commentary on expert evidence, most prominently in the Court of Appeal’s judgment in Duffy v McGee, has been almost entirely on reinforcing the expert’s substantive duty of independence and objectivity within the existing adversarial framework.¹⁶ The courts have been more vocal about what an expert must

be (independent, objective, impartial) than about how their evidence should be heard.

This reveals a bifurcation in the reform process. The Law Reform Commission pursued a path of legislative reform focused on the fundamental duties and status of the expert. In parallel, the Superior Courts Rules Committee, a body primarily composed of judges and practitioners, pursued a procedural path focused on providing new case management tools. The fact that the “debate amongst experts” was introduced via a court rule in the same year that the LRC omitted it from its legislative proposals is telling. It indicates a preference within the judiciary for handling this type of innovation through flexible, discretionary court rules rather than through a rigid, one-size-fits-all legislative mandate. This approach allows judges to deploy the tool on a case-by-case basis where they deem it appropriate, without imposing a wholesale procedural revolution on the entire system. The “debate amongst experts” thus remains a specialised instrument in the judicial toolkit, available for complex cases, but not one that has been widely promoted or frequently deployed in the years since its creation. Its evolution remains quiet, driven by judicial discretion rather than legislative imperative.

Part V: A Multi-faceted Analysis of Concurrent Expert Evidence

The decision to adopt a procedure like CCE involves a complex series of trade-offs that affect each of the key participants in the trial process differently. An analysis of the international experience, particularly from jurisdictions where hot-tubbing is more common, reveals a nuanced picture of its advantages and disadvantages for the court, the parties and their legal counsel, and the expert witnesses themselves.

5.1. The Court’s Perspective

For the judiciary, CCE is primarily seen as a tool to enhance comprehension and improve the quality of judicial decision-making in technically complex cases.

Pros:

• Enhanced Comprehension and Clarity: This is the most frequently cited benefit for judges. By hearing experts discuss and debate the issues directly with each other, the judge can gain a much clearer and more immediate understanding of the core technical disagreements.⁵ The process allows the judge to see, in real-time, how different assumptions lead to different conclusions and to compare competing methodologies side-by-side. The ability for the judge to take an active role, ask clarifying questions on the spot, and moderate the discussion is a powerful aid to understanding.¹
• Increased Efficiency and Time Savings: CCE can lead to considerable savings in court time. The pre-trial conclave and joint report process significantly narrows the issues, meaning the hearing can focus exclusively on the areas of real dispute.⁵ The concurrent session itself is often shorter than sequential cross-examinations of multiple experts.¹
• Improved Quality of Evidence: The process is believed to improve the quality of the evidence presented. The prospect of a direct, professional debate with a peer can temper extreme or partisan opinions. Experts are less likely to advance untenable positions when they know they will be immediately challenged by a knowledgeable colleague, rather than by a lawyer who may lack the same technical expertise. This leads to a reduction in the prevalence of “pseudo-experts” or biased “hired guns”.¹⁰
• Greater Judicial Control: The procedure gives the judge greater control over the presentation of expert evidence, allowing them to set the agenda and ensure the discussion remains focused on the issues that are most important for the resolution of the case.⁷

Cons:

• The “Battle of the Orators”: A significant risk is that the judge may be unduly swayed by the expert who is more articulate, persuasive, or personally impressive, rather than the expert whose opinion is more scientifically sound. The process could favour the better debater over the better expert.⁵
• Inconsistent Judicial Application: The success of CCE is heavily dependent on the skill and approach of the presiding judge. The research notes that judges are not uniform in their approach; some take a very active, interventionist role, while others are more passive and leave the questioning largely to counsel. This inconsistency can create uncertainty for the parties and experts about how the session will be conducted.³⁶
• Risk of Unstructured Debate: If not managed firmly by the judge, the concurrent session risks degenerating into a rambling, unfocused discussion that creates more confusion than clarity. It requires active and skilled chairing by the judge to keep the process on track.¹⁰

5.2. The Parties’ (and Counsel’s) Perspective

For the litigants and their legal teams, CCE presents a mixture of practical benefits and a significant loss of traditional adversarial control.

Pros:

• Cost and Time Savings: The efficiency gains of CCE can translate directly into cost savings for the parties. Narrowing the issues pre-trial and shortening the hearing reduces legal fees and expert witness fees.¹
• Improved Case Assessment and Settlement Prospects: The joint report produced after the expert conclave is a powerful tool for case assessment. It provides the parties with a clear, objective summary of the expert dispute, highlighting the strengths and weaknesses of their respective positions. This clarity can facilitate more realistic and earlier settlement negotiations.¹
• More Focused Advocacy: By crystallising the points of disagreement, the joint report allows legal counsel to focus their preparation and any subsequent questioning on the critical issues that will decide the case, rather than wasting time and resources on matters that are ultimately agreed or peripheral.⁹

Cons:

• Loss of Adversarial Control: This is perhaps the most significant drawback from the perspective of many trial lawyers. CCE diminishes the control that counsel has over the presentation of evidence. The traditional, carefully structured cross-examination is replaced by a more fluid, judge-led discussion. This is often viewed as a dilution of the adversarial process and an infringement on counsel’s ability to strategically test the opposing expert’s evidence.⁵
• High-Risk Pre-Trial Conclave: The expert conclave, held without the presence of lawyers, is a source of considerable anxiety for instructing solicitors. An expert who is not thoroughly prepared or who is overly conciliatory could make an unhelpful or damaging concession that irrevocably harms their party’s case before the trial has even begun.⁵
• Difficulty in Challenging Credibility: The collegiate atmosphere of a concurrent session makes it practically very difficult to conduct a traditional, aggressive cross-examination aimed at challenging the credibility or credit of an expert witness. While some judges view this as an advantage that fosters professionalism, it can be a disadvantage for a party that has a legitimate reason to question an expert’s bona fides.³⁶

5.3. The Experts’ Perspective

For the expert witnesses themselves, the experience of CCE is often viewed positively, as it aligns more closely with their professional norms of dialogue and debate.

Pros:

• A More Professional and Collegiate Forum: Many experts report a strong preference for CCE because it allows them to engage in a professional discussion with their peers, rather than enduring what can often feel like a hostile and unconstructive cross-examination by lawyers who may not fully grasp the technical nuances of their field.⁹
• Opportunity for Fuller and Clearer Expression: Experts often feel that CCE gives them a better opportunity to fully and accurately explain their opinions. They are less constrained by the narrow, often leading, questions of a cross-examiner and have the freedom to elaborate on their reasoning and respond directly to the points made by their colleagues, effectively removing the “lawyer filter”.⁵
• Reinforcement of Independence: The process structurally reinforces the expert’s true role as an impartial assistant to the court. By engaging directly with the judge and their peers, they are positioned as educators rather than as partisan advocates, which many find to be a more comfortable and professionally appropriate role.⁹

Cons:

• The “Alpha” Expert Problem: The dynamic of the hot tub can be influenced by the personalities and professional standing of the experts involved. There is a risk that a more junior, less experienced, or less assertive expert may feel intimidated and defer to the views of a more senior or dominant expert in the room, particularly if they have a pre-existing professional relationship.¹⁰
• Requirement for New Skill Sets: Success in a hot tub requires more than just technical expertise. It demands strong oral communication, active listening, and debating skills. An expert who is a brilliant scholar but a poor communicator may find themselves at a disadvantage in this dynamic environment.¹
• Risk of Unprofessionalism: The less formal and more conversational nature of the hot tub, compared to traditional testimony, carries a risk that experts may drop their professional guard. There is a danger that the discussion could become overly personal or that experts might use non-professional language, forgetting the formality of the court setting.¹

Comparative Analysis of Concurrent Expert Evidence: Advantages and Disadvantages for Key Stakeholders

Stakeholder	Advantages	Disadvantages
The Court	– Enhanced Comprehension: Allows for direct, real-time comparison of complex opinions and methodologies.5	– Increased Efficiency: Saves considerable hearing time by focusing on disputed issues.1	– Issue Narrowing: The pre-trial joint report process crystallises points of agreement and disagreement.5	– Improved Evidence Quality: Discourages partisan or extreme opinions (“hired guns”) through peer scrutiny.10	– Influence of Personality: Risk of being swayed by the more articulate or dominant expert, rather than the most meritorious opinion.5	– Inconsistent Judicial Approach: Lack of uniformity in how judges manage the session creates uncertainty.36	– Risk of Unstructured Debate: Requires strong judicial management to prevent the discussion from becoming rambling and confusing.10
The Parties / Counsel	– Cost Savings: Reduced trial time and focused preparation can lead to lower legal and expert fees.1	– Clearer Case Assessment: The joint report provides a clear view of the case’s strengths and weaknesses, aiding settlement.1	– Focused Advocacy: Allows counsel to concentrate on the critical points of disagreement.9	– Loss of Adversarial Control: Counsel cedes control over the examination of their expert to a judge-led discussion, diluting adversarial strategy.5	– Risk of Pre-Trial Concessions: The lawyer-free conclave creates a risk of an expert making a damaging admission.5	– Difficulty in Challenging Credit: The collegiate format makes it very difficult to conduct a traditional cross-examination on an expert’s credibility.36
The Experts	– Professional Dialogue: Allows for a more collegiate discussion with peers, which is often preferred to hostile cross-examination.9	– Fuller Expression of Opinion: Provides a better opportunity to explain complex reasoning without the constraints of a lawyer’s questioning.5	– Reinforces Independence: Structurally supports the expert’s role as an impartial educator of the court.9	– The “Alpha” Expert Problem: A more junior or less assertive expert may feel pressured to defer to a more dominant colleague.10	– Requires New Skills: Demands strong debating and communication skills beyond pure technical expertise.1	– Risk of Unprofessional Conduct: The less formal setting carries a risk of experts losing their professional composure.1

Part VI: Comparative Perspectives: Lessons from Abroad

6.1. The Australian Model: The Pioneer

Any analysis of CCE must begin with Australia, the jurisdiction where the procedure was born and has reached its most mature state of development. The Australian experience provides the most comprehensive body of evidence on the long-term application and effects of hot-tubbing. The procedure is now an entrenched feature of the rules and practice notes in various Australian courts, particularly the Federal Court of Australia.⁵

Key features of the Australian model, as detailed in the research, include its inherent flexibility, allowing judges to adapt the process to the specific needs of each case, and the centrality of the pre-trial “conclave” and subsequent joint report.⁵ This pre-trial phase is considered an essential element of the process, designed to ensure that the in-court hearing is as focused and efficient as possible. A crucial cultural and legal factor underpinning the success of the model in Australia is that expert witnesses, much like lawyers, are understood to have an explicit and overriding duty to the court. This duty provides the judge with the necessary authority to control the agenda and guide the experts towards a productive dialogue focused on assisting the court.⁵

The reception of CCE among the Australian judiciary has been overwhelmingly positive. Judges have consistently reported that the procedure is a far more effective tool for understanding complex technical evidence compared to the traditional adversarial method. They see it as a significant time-saver and a powerful mechanism for getting to the heart of the technical dispute.⁵ This strong judicial endorsement has been a key driver of its widespread adoption and integration into Australian legal culture.

6.2. The UK Approach: A Flexible Toolkit

The experience of England and Wales offers another valuable comparative perspective, particularly as its legal system shares many historical and procedural similarities with Ireland’s. The UK has adopted CCE, but has done so in a characteristically pragmatic and flexible manner. The procedure is provided for under Practice Direction 35 of the Civil Procedure Rules (CPR).⁷

Following a review by the Civil Justice Council, the rules were amended to clarify and enhance this flexibility. The current UK approach explicitly rejects a “one-size-fits-all” model. The amended PD 35 makes it clear that CCE is not the default position for all expert evidence. Instead, it is one of several options in a “toolkit” available to the trial judge.³⁹ The court has the discretion to order:

1. Traditional sequential cross-examination.
2. Full concurrent evidence (“hot-tubbing”).
3. A hybrid “issue-by-issue” basis, where experts from each side give their evidence on a single issue before moving to the next, allowing for a more focused, back-to-back comparison without a full hot tub.³⁹

This flexible approach is a key lesson for other jurisdictions, including Ireland. It demonstrates that the choice is not a binary one between the old adversarial system and a full CCE model. Instead, procedural tools can be blended and adapted to suit the particular circumstances of the case, the nature of the expert dispute, and the preferences of the trial judge. The use of CCE in the UK has been noted in specific types of complex litigation, such as high-value construction disputes, competition law cases, and some medical negligence claims, mirroring the areas where the procedure is considered most valuable in Australia.⁸

The international experience, from the mature model in Australia to the flexible toolkit in the UK, underscores a critical point: the successful implementation of CCE is not merely a matter of changing a rule on a page. It is deeply intertwined with the prevailing legal culture and, most importantly, the active engagement and training of the judiciary. The procedure’s success hinges on the judge’s ability and willingness to transition from a passive umpire to an active moderator. Without this judicial buy-in and the development of the necessary skills to manage the process effectively, the risks of the procedure—such as unstructured debates or the dominance of personality—can outweigh its benefits. The cautious and limited uptake in Ireland to date may, in part, be a reflection of the absence of the cultural and institutional infrastructure, including dedicated judicial training, that has supported its more widespread adoption elsewhere.

Part VII: Conclusion and Future Outlook for CCE in Ireland

7.1. Synthesizing the Findings: A Mechanism, Not a Movement

This analysis of Concurrent Expert Evidence within the Irish legal context leads to a clear and nuanced conclusion. While Ireland has, since 2016, possessed a formal mechanism for CCE through the “debate amongst experts” procedure provided for in the Rules of the Superior Courts, there is little evidence to suggest a widespread movement towards its adoption. The Irish “hot tub” exists on paper, but it is not yet a common feature of the litigation landscape. It remains a niche and discretionary tool, confined to specific categories of complex commercial litigation and, according to available commentary, infrequently deployed even within those confines.

The Irish approach has been one of caution and incrementalism. The legislature and the Rules Committee have provided the judiciary with a modern case management tool but have deliberately limited its scope, most notably by excluding the vast area of personal injury litigation. The focus of legal reform and judicial commentary has remained predominantly on reinforcing the substantive duties of the expert—their independence, objectivity, and overriding duty to the court—rather than on revolutionising the procedure by which their evidence is heard. Therefore, the current state of play is one of potential rather than practice. The tap has been turned on, but the tub is far from full.

7.2. Barriers to Wider Adoption in Ireland

Several significant barriers appear to be constraining the wider adoption of CCE in Ireland. These obstacles are a combination of cultural, practical, and institutional factors:

• Deep-Rooted Adversarial Culture: The Irish legal system, and particularly the culture of the Bar, is deeply rooted in the adversarial tradition. CCE requires a significant ceding of control from counsel to the judge, a shift that can be uncomfortable for advocates trained in the art of strategic cross-examination. This cultural resistance to a more inquisitorial style of proceeding is likely a primary impediment.⁵
• Lack of Judicial Precedent and Familiarity: The scarcity of reported cases where the “debate amongst experts” has been used creates a cycle of uncertainty. Practitioners may be hesitant to propose a procedure with which they are unfamiliar, and judges may be reluctant to order a process for which there is little guiding precedent. This lack of familiarity on both sides of the bench fosters a natural inclination to stick with the traditional, well-understood method.
• Practical and Skill-Based Hurdles: The procedure demands new skills from all participants. Judges must become adept moderators, and experts need strong communication and debating abilities in addition to their technical knowledge.¹ Furthermore, the practical challenges of organising pre-trial conclaves among busy professionals can be a significant logistical barrier.³⁶
• Divergent Reform Focus: As identified, the reform agenda in Ireland has been bifurcated. The Law Reform Commission has focused on the legislative framework governing expert duties and accountability, while the Rules Committee has focused on procedural tools. Without a unified push from a body like the LRC to champion CCE as a primary reform objective, it is likely to remain a secondary case management option rather than a central feature of the system.

7.3. Recommendations for Practice and Future Evolution

Despite the slow uptake, the potential benefits of CCE in terms of efficiency, clarity, and improved judicial comprehension remain compelling, particularly in an era of increasingly complex and costly litigation. For the Irish legal system to more fully realise this potential, a more structured and proactive approach to the evolution of the “debate amongst experts” procedure could be considered. Several potential steps could foster greater confidence and use:

1. A Dedicated Practice Direction: The judiciary could consider issuing a formal Practice Direction dedicated specifically to the conduct of the “debate amongst experts.” Drawing on the detailed guidance available in the UK’s CPR PD 35, such a direction could provide much-needed clarity and consistency on the procedure, outlining the steps for initiating the process, the format of the joint report, and the ground rules for the in-court debate. This would reduce uncertainty for practitioners and judges alike.
2. Judicial Training and Education: A concerted effort in judicial training would be invaluable. Workshops and seminars focused on the practical skills required to effectively chair a concurrent evidence session would equip judges with the confidence and techniques to manage the process effectively, mitigating the risks of unstructured debate or personality dominance.
3. Pilot Programmes: To build familiarity and gather empirical data on the procedure’s effectiveness in the Irish context, the Courts Service could consider establishing pilot programmes to test the “debate amongst experts” in a wider, but still controlled, range of non-jury cases. This would allow the judiciary and the legal profession to gain practical experience with the mechanism in a structured way.

The “hot tub” may never be suitable for every case, and the traditional adversarial process will always have its place. However, the “debate amongst experts” represents a valuable and modern tool in the court’s case management arsenal. It offers a potential solution to some of the most persistent problems associated with the use of expert evidence in complex litigation. While its journey into the mainstream of Irish legal practice has been slow, with careful management, clear guidance, and a willingness to embrace procedural innovation, it has the potential to become a significant contributor to the fair, efficient, and effective administration of justice in Ireland.

Works cited

1. Hot-tubbing of the experts – Arbitration – iPleaders, accessed on July 11, 2025, https://blog.ipleaders.in/hot-tubbing-experts/
2. What Constitutes Bias in an Expert Witness? – Advise & Consult, Inc., accessed on July 11, 2025, https://www.myconstructionexpert.com/blog/expert-witness-what-constitutes-bias/
3. Experts: Concurrent expert evidence (Hot-tubbing) – Practical Law, accessed on July 11, 2025, https://uk.practicallaw.thomsonreuters.com/w-040-7544?transitionType=Default&contextData=(sc.Default)
4. Hot-tubbing (Concurrent Evidence) – The Expert’s Friend? | HKA, accessed on July 11, 2025, https://www.hka.com/article/hot-tubbing-the-experts-friend/
5. Experts in a Hot Tub – Testifying Concurrently as an Expert Witness …, accessed on July 11, 2025, https://www.alvarezandmarsal.com/insights/experts-hot-tub-testifying-concurrently-expert-witness
6. The expert hot tub: choose your model – Oxera, accessed on July 11, 2025, https://www.oxera.com/insights/agenda/articles/the-expert-hot-tub-choose-your-model/
7. Concurrent Evidence – The Academy of Experts, accessed on July 11, 2025, https://academyofexperts.org/users-of-experts/concurrent-evidence/
8. CJC Concurrent Expert Evidence and Hot-Tubbing in English Litigation Since the Jackson Reforms – Judiciary.uk, accessed on July 11, 2025, https://www.judiciary.uk/wp-content/uploads/2011/03/cjc-civil-litigation-review-hot-tubbing-report-20160801.pdf
9. Concurrent Expert Evidence – A Novel Evidentiary Device – SCC Online, accessed on July 11, 2025, https://www.scconline.com/blog/post/2022/09/08/concurrent-expert-evidence-a-novel-evidentiary-device/
10. That litigation technique called hot tubbing: what’s so hot about it? | Asia IP, accessed on July 11, 2025, https://www.asiaiplaw.com/article/that-litigation-technique-called-hot-tubbing-whats-so-hot-about-it
11. Guide to Concurrent Evidence in New South Wales – ExpertsDirect, accessed on July 11, 2025, https://expertsdirect.com/guide-to-concurrent-evidence-in-new-south-wales/
12. Expert Evidence – Irish Legal Blog, accessed on July 11, 2025, https://legalblog.ie/37346-2/
13. The expert – Law Society of Ireland Gazette, accessed on July 11, 2025, https://www.lawsociety.ie/gazette/in-depth/2024/february/the-expert/
14. The Expert Witness and Wasted Costs Orders – Solicitor’s Beware! | Flynn O’Driscoll | FOD, accessed on July 11, 2025, https://www.fod.ie/news/the-expert-witness-and-wasted-costs-orders—solicitors-beware
15. The role of the expert witness – Medisec Ireland, accessed on July 11, 2025, https://medisec.ie/wp-content/uploads/2024/04/2023.12.19-MINDO-Role-of-expert-witness.pdf
16. Restricted Role of Expert Witnesses Confirmed – Mason Hayes Curran, accessed on July 11, 2025, https://www.mhc.ie/latest/insights/restricted-role-of-expert-witnesses-confirmed
17. The Role of The Expert Witness – MHP Sellors, accessed on July 11, 2025, https://mhpsellors.ie/the-role-of-the-expert-witness/
18. Duties of expert witnesses – Part II – Engineers Ireland, accessed on July 11, 2025, https://www.engineersireland.ie/Brexit/duties-of-expert-witnesses-part-ii
19. Expert Evidence – Irish Legal Blog, accessed on July 11, 2025, https://legalblog.ie/expert-evidence-2/
20. The Chartered Surveyor as Expert Witness A Guide to Best Practice, accessed on July 11, 2025, https://scsi.ie/wp-content/uploads/2022/04/expert_witness_best_practice_.pdf
21. High Court on Expert Witness Role in Litigation | Hayes SolicitorsHayes solicitors LLP, accessed on July 11, 2025, https://hayes-solicitors.ie/news/recent-high-court-consideration-of-the-role-of-the-expert-witness-in-litigation/
22. Summary of New Superior Court Rules | Hayes Solicitors LLP, accessed on July 11, 2025, https://hayes-solicitors.ie/news/new-rules-of-the-superior-courts-a-brief-summary/
23. S.I. No. 254/2016 – Rules of the Superior Courts (Conduct of Trials) 2016., accessed on July 11, 2025, https://www.irishstatutebook.ie/eli/2016/si/254/made/en/print
24. New High Court Rules Strive for Efficiency and Expediency – Fieldfisher, accessed on July 11, 2025, https://www.fieldfisher.com/en-ie/locations/ireland/ireland-blog/new-high-court-rules-strive-efficiency-expediency
25. A question of evidence – New Rules of the Superior Courts – Law Society, accessed on July 11, 2025, https://www.lawsociety.ie/news/news/Stories/A-question-of-evidence–New-Rules-of-the-Superior-Courts
26. The Actuary as Expert Witness, accessed on July 11, 2025, https://web.actuaries.ie/sites/default/files/asp/ASP%20EXP-1/ASP%20EXP-1%20-%20The%20Actuary%20as%20Expert%20Witness.pdf
27. High Court judgment confirms Expert Witness needs to demonstrate to the Court that he/she is an Expert if his/her evidence is to be even considered – Friel Stafford, accessed on July 11, 2025, https://frielstafford.ie/high-court-judgment-confirms-expert-witness-needs-to-demonstrate-to-the-court-that-he-she-is-an-expert-if-his-her-evidence-is-to-be-even-considered/
28. Energy Disputes 2017 – Matheson, accessed on July 11, 2025, https://www.matheson.com/docs/default-source/practice-area-attachments/energy-and-natural-resources/energy_disputes_2017.pdf?sfvrsn=9de81659_1
29. OPINION AND EXPERT EVIDENCE IN FAMILY LAW PROCEEDINGS, accessed on July 11, 2025, https://familylawyers.ie/wp-content/uploads/2022/10/EXPERT-EVIDENCE-.pptx
30. Changing and Exchanging Expert Reports – WILLIAM FRY, accessed on July 11, 2025, https://www.williamfry.com/knowledge/changing-and-exchanging-expert-reports/
31. Expert Evidence – Law Reform Commission, accessed on July 11, 2025, https://www.lawreform.ie/_fileupload/consultation%20papers/cpexpertevidence.pdf
32. Law of Evidence – Law Reform Commission, accessed on July 11, 2025, https://www.lawreform.ie/welcome/law-of-evidence.204.html
33. Report on Consolidation and Reform of Aspects of the Law of Evidence, accessed on July 11, 2025, https://www.lawreform.ie/news/report-on-consolidation-and-reform-of-aspects-of-the-law-of-evidence.705.html
34. Law Reform Commission: Report on the Consolidation and Reform of Aspects of the Law of Evidence | Fieldfisher, accessed on July 11, 2025, https://www.fieldfisher.com/en-ie/locations/ireland/ireland-blog/law-reform-commission-report-consolidation-reform-aspects-law-evidence
35. Expert Evidence: The Challenges of Complexity Delivered by Mr. Justice Maurice Collins at the 22nd Annual Grange Conference on 2 – Family Law, accessed on July 11, 2025, https://services.courts.ie/docs/default-source/default-document-library/collins-j.-expert-evidence—the-challenges-of-complexity.pdf
36. Reflections on concurrent expert evidence – AustLII, accessed on July 11, 2025, https://www8.austlii.edu.au/au/journals/NSWBarAssocNews/2011/75.pdf
37. Hot-tubbing | Practical Law – Thomson Reuters, accessed on July 11, 2025, https://uk.practicallaw.thomsonreuters.com/7-528-7847?transitionType=Default&contextData=(sc.Default)
38. PRACTICE DIRECTION 35 – EXPERTS AND ASSESSORS – Civil Procedure Rules – Justice.gov.uk, accessed on July 11, 2025, https://www.justice.gov.uk/courts/procedure-rules/civil/rules/part35/pd_part35
39. Amendments to CPR Practice Direction 35.11 – Bond Solon, accessed on July 11, 2025, https://www.bondsolon.com/news-and-insights/amendments-to-cpr-practice-direction-3511/