What is hot-tubbing?

Expert evidence on the technical aspects of a matter and the credibility of the expert can be crucial in determining the outcome of a case. New provisions in the rules of court now seek to promote a ‘menu’ of options available for giving oral expert evidence at court, in particular the use of ‘hot-tubs.’

The court has had the ability to direct that some or all of the experts from like disciplines give evidence concurrently for a number of years. This process is otherwise known as “hot-tubbing”, because it involves several experts being present in court at the same time. In this way, hot-tubbing differs to the more traditional approach where an expert is examined and cross-examined individually by a party’s barrister. The new provisions in the rules of court lend support to an increase in the use of hot tubs.


Supporters of hot-tubbing say that having experts questioned at the same time by a judge, who evaluates their evidence, enables the issues in dispute to be narrowed. It has found favour with the judiciary too. In a Scottish case, where six tunnelling experts and a geologist were in court at the same time, the judge commented that he had found the process a “valuable way of focussing on the main issues and assessing the quality of their [the experts’] contributions”. The judge chaired their discussion and imposed time limits on individual contributions. As a result, the judge “was able to hear the different opinions at one and the same time. They [the experts] were also able to challenge one another’s position. This brought the topics into sharp focus. Each expert had to crystallise his position.”

Is hot-tubbing here to stay?

Hot-tubbing will not always be suitable for every case. Those who oppose hot tubbing point to the fact that a party’s barrister often has little opportunity to question the expert directly, and that some experts may make concessions too readily. Support for the use of hot tubs gained momentum with the publication last year of the Civil Justice Council’s snappily entitled report “Concurrent expert evidence and “hot tubbing” in English litigation since the “Jackson reforms”: legal and empirical study”.

The report, which has subsequently been considered by the Civil Procedure Rule Committee, made a number of recommendations to encourage the use of concurrent evidence where appropriate. Whilst not advocating the use of hot-tubbing in all cases, the Committee approved an amendment to the existing Practice Direction so that in the future the court will be able to set the agenda for the giving of concurrent evidence. The Committee also signalled that even where concurrent evidence is not given, the court may direct the manner in which expert evidence is to be provided. For example, the court may direct that experts from like disciplines give their evidence and be cross-examined on an issue-by-issue basis, followed consecutively by other experts giving evidence in relation to the same issue. The changes to the Practice Direction are now in force, having been formally approved on 21 November 2017.


In my view ‘hot-tubbing’ can be an extremely valuable exercise. Instead of hearing complex expert testimony weeks apart, the ultimate decision maker is in a position to hear the different opinions at one and the same time. It follows that the experts will need to rise to the challenge offered by ‘hot-tubbing’, providing crisp answers. I suspect that the exercise will be less successful where there is little common ground and/or the level of detail is just too great. Although it is unlikely that there will be sudden increase in the use of hot tubbing in the immediate future, support for its use may now be encouraged by the judiciary and the courts.