Forensic experts from all disciplines, accounting, engineering, digital forensics, and economics, should be prepared for hot-tubbing in any complex dispute, particularly in the TCC and CAT.
What Is Hot-Tubbing?
Hot-tubbing, formally concurrent evidence, is a procedure where experts from both sides give evidence simultaneously before the judge or tribunal, rather than in the traditional sequential format of examination-in-chief followed by cross-examination.
The judge or arbitrator directs the discussion, asking questions, probing areas of agreement and disagreement, and inviting experts to respond to each other's opinions in real time. This allows the tribunal to directly compare expert evidence and resolve technical questions more efficiently.
Hot-tubbing was pioneered in Australian courts and has been increasingly adopted in the UK, particularly in the Technology and Construction Court, the Competition Appeal Tribunal, and international arbitration.
When Is Hot-Tubbing Ordered?
Courts and tribunals order hot-tubbing where expert evidence is central to the dispute and traditional cross-examination would be inefficient or ineffective. It is particularly common in: TCC construction disputes involving quantum and delay experts; CAT competition proceedings involving economic experts; digital forensics cases with highly technical evidence; and international arbitration under ICC and LCIA rules.
The court may order hot-tubbing of its own initiative or on application by either party. CPR Part 35 and the TCC Guide support the use of concurrent evidence in appropriate cases. Tribunals in international arbitration frequently use hot-tubbing as standard practice for expert evidence.
TCC and Arbitration Practice
In TCC proceedings, hot-tubbing typically follows the exchange of expert reports and a joint statement identifying agreed and disputed issues. The experts are sworn in together and the judge directs the discussion, with advocates permitted to ask supplementary questions.
In international arbitration, hot-tubbing is commonly used under IBA Rules on Evidence. The tribunal may structure the session by issue, asking each expert to address specific questions before inviting discussion between the experts.
The format varies, some tribunals prefer a structured question-and-answer approach, while others allow freer discussion. Experts should be prepared for both formats.
Preparing Forensic Experts for Hot-Tubbing
Preparation for hot-tubbing begins with the joint expert meeting and joint statement. Experts must have clearly identified the areas of agreement and disagreement before the hot-tubbing session, with reasons for any remaining disputes documented.
Experts should be prepared to: explain their methodology clearly and concisely; respond directly to the opposing expert's opinions; acknowledge areas of agreement without compromising their position on disputed issues; and answer the judge's or tribunal's questions directly and honestly.
Advocates should brief their experts on the hot-tubbing format, the likely areas of focus, and the importance of addressing the tribunal directly rather than through counsel.
Joint Statements Before Hot-Tubbing
CPR Part 35 requires experts to meet and produce a joint statement identifying agreed facts and opinions, areas of disagreement, and the reasons for disagreement. The joint statement is the foundation for an effective hot-tubbing session.
A well-prepared joint statement narrows the issues significantly, allowing the hot-tubbing session to focus on the genuinely disputed matters rather than rehashing areas of agreement.
In multi-discipline cases, separate joint statements are produced within each discipline. Coordinate joint meetings across disciplines where issues overlap, for example, where the quantum expert's calculations depend on the delay expert's EOT assessment.