Experts giving evidence concurrently in court – known as hot-tubbing – is improving quality, saving trial time and helping judges determine disputed issues, the first study of the practice since it was introduced in 2013 has found.
A Civil Justice Council working group also highlighted a series of improvements that would help encourage hot-tubbing, including a re-drafted version of the practice direction, a new guidance note for judges and practitioners, and an information note for expert witnesses.
Its newly published report  suggested that some further amendment of court guides, and some judicial training, may provide further consistency and familiarity with the procedure of hot-tubbing – “albeit with the overriding caveat that the technique will not be for every case”.
The working group was chaired by Professor Rachael Mulheron of Queen Mary University of London and a member of the CJC.
It found that hot-tubbing had been used in a wide variety of cases, from the Court of Protection to competition law.
There were variations on how it was done. In some cases, experts gave evidence back-to-back, while ‘pure’ hot-tubbing involved the judge-led joint examination of experts.
The report identified “hybrid” versions depending on the role that counsel was permitted to play during the hot-tubbing; different judicial attitudes towards the interaction among expert witnesses whilst they are in the hot-tub; and differences in judicial practice, in that the judge would not always lead the discussion.
Though not strictly within its remit, the working group also looked at the ‘teach-in’ type approach that has been employed in some cases, which sees the court appoint a ‘neutral scientific adviser’ to provide a tutorial, or ‘teach-in’, on the technical issues arising in the case.
In one High Court patent case, the adviser’s instructions were settled by the court; she was not informed about the specific issues in the case, but gave ‘high-level’ assistance; she was asked to prepare materials (primarily Powerpoint slides) to educate the court on five topics; and she met with the judge for one day, for a ‘candid discussion’.
The parties and their representatives were not present during the ‘teach-in’, but were provided with a copy of the relevant papers afterwards, in the interests of transparency. The adviser did not sit in court for the trial itself.
The report said that “perhaps the most interesting, and positive, outcome” of the project – which included surveys of judges, practitioners and experts – was the finding that 83% of judicial respondents considered that the quality of the expert evidence was improved, where it was given via hot-tubbing.
Lawyers were similarly positive, although the figure fell to 60% among experts.
“Even more overwhelmingly supportive were the judiciary responses as to whether hot-tubbing assisted the court to determine disputed issues of expert evidence. 100% of respondents said that it did.”
The vast majority of lawyers agreed, as did 71% of experts, although “for those who had been ‘hot-tubbed’, the experience led to some reservations”, the report noted.
Judges and experts also thought hot-tubbing reduced trial length, but lawyers, though a majority agreed, were more sceptical. The more negative views may have been driven by the degree of cross-examination by counsel which was permitted to follow (or even precede) the hot-tubbing, the report said.
However, the final goal of hot-tubbing identified by Sir Rupert Jackson when he recommended it – saving costs – was “the one area where the majority of the legal respondents to the survey seemed to be of one mind”, namely it was not really achieving that. The working group suggested more work might be needed to work out why.
The report said: “In the view of the working group, the current PD 35.11 has served an important purpose, in both drawing to the attention of courtroom participants the process of hot-tubbing, and by providing a framework for that process, especially when it was such a novel procedure.
“However… it seems apposite that the PD should be revised to reflect/record that hot-tubbing is but one form of concurrent expert evidence; that sequential, back-to-back, evidence is another important format of concurrent evidence; that the ‘teach-in approach’ has great benefits for the right type of case; and that, above all, the court may give directions for any of these processes to be used at trial.
“The working group also considered that, in light of the variations in practice surrounding the role of counsel after the judge-led examination concludes, it would be helpful to set out the circumstances in which further questioning should be permitted by the court.”
The guidance note for judges and practitioners would supplement the revised PD and set out briefly the different ways in which expert opinion evidence can be adduced, and identify factors which might indicate whether a direction for judge-led joint expert examination might be appropriate.
The working group also recommended a series of measures to improve familiarity with, and education about, concurrent evidence in general, and hot-tubbing in particular, such as the information note for experts, a training DVD, and inserting a further question in the listing questionnaire, directions questionnaire, and case management information sheet asking: “Do you consider that any part of the oral expert evidence should be given concurrently (see PD 35, para 11)?”