The usual procedure in trials in the courts of England and Wales is that when hearing expert evidence, each expert witness is sworn into the witness box individually and, then each one is cross-examined in turn by the opposing counsel. Since 1 April 2013, however, a judge can, at any stage of the proceedings, order concurrent expert evidence to be given at trial pursuant to paragraph 11 of CPR Practice Direction 35 (also known as "hot-tubbing") where expert witnesses (of the same discipline) are sworn into the witness box at the same time. The judge then engages in discussion with the experts dealing with the issues in dispute. The parties' representatives may also join the discussion and, subject to the judge's permission being obtained, put questions to the experts.

The procedure is commonly used in Australia, but has not gained as much support in England and Wales. The question is why? This article considers some of the advantages and disadvantages of hot-tubbing and its future in England and Wales.


The purpose of hot-tubbing is to enable a discussion to take place between the experts which assists the judge working through (1) the issues in dispute and (2) each expert's opinion and reasoning. Open questions are used to allow the experts to discuss the issues, which differs significantly from the questioning technique used in cross-examination. It is believed that experts are likely to be more willing to concede points in hot-tubbing than they would be in cross-examination, where experts can be defensive.

As discussions are led by the judge, from an early stage the judge needs in-depth knowledge, requiring the judge to thoroughly read the documents and to understand the issues in dispute prior to the trial.

For hot-tubbing to be effective, there is a lot of groundwork that the lawyers and experts need to undertake. The advantage is that there is greater focus on the issues in dispute and parties may be able to narrow the issues in the lead-up to trial.

Finally, supporters of hot-tubbing believe it reduces the time for expert evidence at trial and therefore the length and costs of trial.


The usual process allows counsel to cross-examine the opposing party's expert and also re-examine its own expert to deal with issues arising out of cross-examination. Arguably, counsel is better placed to question experts, having extensively prepared for the trial. By not cross-examining experts, counsel may be deprived of making some of the points and may be unable to take the experts and the judge to certain documents to make those points.

It may be hard to determine when hot-tubbing is appropriate. Some commentators have stated that hot-tubbing is not necessarily appropriate in large cases. In one of the largest cases in the Federal Court of Australia, the judge did not use hot-tubbing for the competition expert evidence as there were six experts (Seven Network Limited v. News Limited [2009] FCAFC 166). However, in the recent case between Samsung and Apple, also at the Federal Court of Australia, hot-tubbing was used despite there being numerous experts (Samsung Electronics Co. Limited v. Apple Inc. [2011] FCAFC 156). There is, therefore, no rule as to when hot-tubbing is appropriate. Judges will need to assess the appropriateness of hot-tubbing on a case-by-case basis, and without experience this may be difficult.

The aim of hot-tubbing is to reduce the length of the trial (as occurred in the Samsung/Apple case). But this reduction was due to the strict time limits imposed and it did not reduce the overall costs. Significant time and resources went into the preparation for the hot-tubbing, agreeing joint questions, various conferences with experts and joint reports. Parties were also encouraged to narrow the issues for determination, which meant further work for lawyers and experts, increasing costs. Therefore, although the trial costs were reduced, the overall costs were high.

In England and Wales, where costs budgets are approved at an early stage of the claim (usually the first costs and case management conference), it may be difficult to estimate the extent of the work necessary in preparing for hot-tubbing. The volume of work will depend on the number of issues in dispute and the extent of the inter-party discussions, which will not be known until later on. Although there are provisions to revise costs budgets, these are limited.

Finally, giving evidence is commonly described as stressful and daunting. Even a leading expert in their field may get nervous in the witness box. The issue of hearing experts together is that dominating personalities may take over in the witness box.

Hot-tubbing in England and Wales

In Harrison and others v. Shepherd Homes Ltd and others [2011] EWHC 1811 (TCC), the usual procedure was followed, but after the cross-examination of the experts there was a process of concurrent expert evidence to which the parties consented. The latter process helped the judge by highlighting the extent of agreement and the limited differences. This example of hot-tubbing was used prior to the introduction of the process into the CPR on 1 April 2013.

On 26 June 2016, Jackson LJ gave a lecture on the subject of hot-tubbing and its future. In the lecture, Jackson LJ quoted a TCC circuit judge who uses hot-tubbing "regularly" and is very much in favour of the process.

Jackson LJ also made reference to the recent case of Streetmap. EU Ltd v. Google Inc. [2016] EWHC 253 (Ch) and stated that Mr Justice Roth found that hot-tubbing helped him highlight the areas of disagreement between the experts. Mr Justice Roth stated in his judgment that it "led to a significant measure of agreement" and "a constructive exchange which considerably shortened the time taken by the economic evidence at trial".

The future

Despite the above cases, there still appears to be a lack of support for hot-tubbing in England and Wales. This may be because, upon detailed consideration, practitioners are of the opinion that hot-tubbing is not beneficial. Alternatively, it may be because the legal industry is slow to take up change and has not considered it in any detail. Regardless of the reasons why, however, it is now on the legal agenda.

Over the course of 18 months from April 2016, the Civil Litigation Review Working Group is reviewing various discrete topics, one of which is the topic of "hot-tubbing". To start the process, a survey has been launched to find out about the use of hot-tubbing. At the end of the review, Jackson LJ is hopeful that improvements to the procedure will be proposed.

Jackson LJ predicts that hot-tubbing will become more common in England and Wales. In his view, hot-tubbing is "a cost saving procedure" and he recommends that it should be piloted in England and Wales in cases where all parties (the parties, lawyers, experts and the judge) consent.

Link to Jackson LJ's lecture on 26 June 2016