Is hot-tubbing working? Further to the Civil Justice Council's report on the use of 'hot-tubbing', we consider whether a different approach to expert evidence is likely to gain traction in the English courts.

The report by the Civil Justice Council (the "Report") provides an insight into the way in which the process of concurrent expert evidence (also known as hot-tubbing) is operating, and the popularity and perceived effectiveness of the process. The Report is based on a survey carried out with members of the judiciary, legal practitioners and expert witnesses.

Since 1 April 2013, the English court has been able to order that oral evidence from experts at trial be given concurrently (hot-tubbing). Concurrent evidence is most commonly used in specialist courts, where evidence on highly technical matters is required, and involves experts from each side giving evidence at the same time and in each other's presence with the judge initiating the discussion. The procedure is currently set out in paragraph 11 of Practice Direction 35 of the Civil Procedure Rules.

In practical terms, the experts are sworn in at the same time and respond to questions from both the judge and each other. The process can be used in a hybrid way, for example in conjunction with traditional counsel-led cross-examination; however, the exact format can vary significantly depending on the preference of the judge and the nature of the expert evidence.


The Report concluded that, on the whole, concurrent evidence was capable of significantly reducing trial length, although judicial preparation time may increase. The most significant benefits are to be found in the court's understanding of the expert evidence, principally through a helpful and constructive narrowing of the issues. The process is generally viewed as less adversarial, and it allows experts to engage with each other's evidence and ask questions.


One of the key concerns about concurrent evidence revealed by the survey is the perception of a loss of control: this is likely to be one of the main reasons why the procedure has not been more popular to date.

The Report also highlights the significant preparation time required to enable a judge to be sufficiently well versed in the evidence and issues to be an effective inquisitor. It is observed in the Report that concurrent evidence has been used more extensively in arbitration than litigation: in many cases, arbitrators are chosen for their technical qualifications, and will therefore have a full understanding of the technical issues upon which expert evidence is required and will be well placed to chair a discussion between experts.


The Report identified that more than one approach to concurrent evidence was being adopted by the courts and recommended that this flexibility should be reflected in Practice Direction 35 by including reference to the variety of techniques available. The Report recommended that, in light of the variations in practice surrounding the role of counsel once the judge-led examination had concluded, it would be helpful to set out the circumstances in which further questioning should be permitted by the court. A draft amendment to the Practice Direction has been proposed, which provides that in general a full cross-examination or a re-examination by counsel will be neither necessary nor appropriate.

The Report also recommended the production of a new Guidance Note, which would set out a 'menu' of the options available to the court in relation to expert evidence and would identify factors which might indicate whether a direction for judge-led joint expert examination would be appropriate in a particular case. For example, if a judge does not have sufficient knowledge of the field of expertise in question, judge-led questioning of the expert witnesses is unlikely to be appropriate.


The recommendations of the Civil Justice Council are being considered by the Civil Procedure Rules Committee and a decision has yet to be reached on whether or not the suggested amendments to the Practice Direction should be implemented.

Concurrent evidence will not be appropriate in all cases. There are many valid concerns, including: a more outspoken expert may unfairly dominate a discussion; extended debate may not in fact save court time; increased preparation time by the judiciary may offset any trial length saving; and the process may lack the rigour of cross-examination. However, in an appropriate case, there may be benefits for parties if the expert process can be streamlined and technical issues are better understood by the court.

The general perception remains that hot-tubbing is not being used widely in practice, and there is perhaps little to suggest that this will change in the short term.

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