Practical Law

The first thing to remember is don’t Google it! But don’t panic either, it’s not as bad as it sounds. “Hot tubbing” or “concurrent evidence”, as it is less scarily known, is a method of giving evidence where both experts (or witnesses of fact) sit in the box together and the tribunal chairs a discussion between them.

The format differs from case to case, but the judge or arbitrator will ask questions as part of the discussion and counsel for either side may join in. The parties can also suggest questions for the tribunal to ask.

Why does it matter?

Hot tubbing is already common-place in international arbitration, where it is often used after cross examination. So far it has not impacted on domestic litigation, as it is not currently provided for in the CPR, but watch this space. Jackson LJ carried out research into its use in the Australian courts as part of his costs review and, in his final report, has suggested that it is piloted for expert evidence in court cases where all parties and the judge agree to it.

However, Jackson LJ has not set out a format, and we will have to wait and see whether one is prescribed by the pilot, or whether it is for the judge and the parties to agree upon. Jackson LJ seems to suggest that hot tubbing could be used in place of cross examination.

What’s the theory?

The theory is that the experts are more likely to make concessions and reach a greater degree of agreement in the hot tub than through cross examination. Things are more relaxed, and the experts can take part in a constructive discussion.

Our experience is that because the experts answer questions at the same time, hot tubbing is very effective in helping to identify areas where the experts truly disagree. Unlike cross examination, the tribunal seeks to ask broad questions which elicit helpful answers from the experts.

Also, as each expert is subject to simultaneous peer scrutiny, the risk of misleading answers is reduced and any inaccuracies should be picked up immediately. If there is any confusion or uncertainty, the tribunal can ask questions straight away to clarify the issue.

To make the most of the hot tub, the tribunal needs to be fully prepared: it needs to understand what the contentious areas are and know what it wants to ask the experts.

What are the risks?

Of course, the major concern is the loss of control. For example, your expert may lose his concentration and may also lose the fear that he would experience under cross examination. This may lead him to make concessions that he would not make if he was in the box on his own (and would not make if he thought about the question properly). To reduce this risk, experts need to be thoroughly prepared for the hot tub.

If there is no cross examination, as Jackson LJ seems to suggest, there is a risk that counsel will not have the opportunity to make all the points that they would like to make, particularly if questions from counsel are not permitted as part of the process. Similarly, there is also the risk that key documents might be missed if counsel cannot bring them to the attention of the tribunal.

Will it work for me?

You might consider suggesting hot tubbing, or agreeing to the other side’s suggestion to use it, if:

• You have a strong case and your expert is confident and persuasive (especially where you know he will come across better than the other expert – weak experts are easily exposed in the hot tub).
• Your expert has had previous experience of being in the hot tub (especially if his opposite number hasn’t).
• The issues are complex and you want to give your expert a chance to explain his theories.

If it comes down to a simple choice between the hot tub or cross examination, it might be best to steer clear of the hot tub where the credibility of your opponent’s expert is in issue. Here a tough cross examination will probably be most advantageous.

The extent of hot tubbing in the courts will, of course, depend on the approach taken by any pilot, so it may be a while before you need to take the plunge.