Concurrent Expert Evidence

The use of concurrent expert evidence, informally known as "hot-tubbing", was introduced through the Jackson reforms in 2010 following its positive use in Australia and in International Arbitration. The process ultimately aims to reduce time spent at trial in the discussion of expert evidence and thereby reduce the costs of litigation. This is particularly relevant to clients in the construction industry, who have seen large increases in the number of disputes since the economic downturn. The practice direction to Civil Procedure Rule (CPR) Part 35 now allows courts the discretion to order that concurrent expert evidence - from some or all of the experts from like disciplines - be the preferred method of deciding the issues between parties. This is likely to occur where the difference in opinion between the experts has not been entirely clear to the judge.

In January 2012, a pilot was undertaken at the Manchester Technology and Construction Court and the Mercantile Court to evaluate the effectiveness of concurrent evidence. The pilot found that the use of concurrent evidence had "time and quality benefits" with no evidence of significant disadvantages.

The process for concurrent evidence is outlined at para 11.4 of CPR PD 35 and begins with the experts each producing separate written reports in the usual manner. Subsequent to the expert reports being exchanged, a meeting is held between the experts in order to prepare a joint statement of those issues which are agreed upon and those which remain in dispute. The joint statement is then given to the judge, along with an agreed agenda.

Once at trial, the ‘sequential' procedure of traditional cross-examination has been removed. ‘Hot-tubbing' allows for the experts in proceedings to be sworn in at the same time. The judge, the experts, the parties and the advocates take part in a discussion of the issues in each other's presence. The judge presides over this debate, asking the same questions to both experts in a bid to find a resolution.

Since the introduction of concurrent evidence, practice has revealed the following advantages and disadvantages to the process:-


  • Hot-tubbing is less rigid than the traditional adversarial process, allowing experts to ask questions of each other and respond directly.
  • The expert becomes less partisan, reinforcing the overriding duty that an expert has in assisting the court.
  • Peer scrutiny avoids misleading answers or inaccuracies in expert testimony.
  • Concurrent evidence saves hearing time, thus reducing the cost of litigation.
  • By having a joint statement prepared by the experts, it has become easier for the parties to agree an agenda of disputed issues for discussion at trial.


  • More advantageous to experts of an assertive and confident nature.
  • Counsel may be less able to direct the discussion and may therefore have difficulties in elucidating key points from the experts.
  • Time at court may be reduced, however, the time required to prepare experts for trial may increase.
  • The judge has the discretion to modify the process of hot-tubbing, which means that experts will need advance warning of any changes prior to appearing at trial in order to adequately prepare.

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