Hot Tub Decision Machine

Andrew Pattie

Published by
Andrew Pattie

7th February 2017

So called “Hot-tubbing” refers to the hearing of concurrent evidence from expert witnesses present in court at the same time, rather than the more traditional means of hearing experts sequentially.  The idea is that the judge facilitates  a discussion between experts to determine each opinion in order to deal with technical issues and test the value of evidence.  This practice has become more commonplace in recent times and – perhaps inevitably - there are differing views as to its value.


The 2015 case of SSE Generation Limited v Hochtief Solutions AG was one of the highest value judgements in recent times to go through the Court of Session.  Lord Woolman presided over a £130 million claim in relation to a collapsed tunnel at the Glendoe Hydroelectric Scheme.

The issue was whether the collapse was covered by the Contractor’s All Risk policy which was in the parties’ joint names.  SSE believed that the collapse was due to the work carried out by Hochteif and as such they were liable to fix it, whereas Hochteif believed it had become SSE’s liability and they should claim under the policy.  SSE eventually employed a different contractor to carry out the remedial work and subsequently  raised an action in the Court of Session for payment by Hochteif of the costs.

Lord Woolman’s judgement centred on the wording of the contract with extensive evidence being heard throughout the case.

Expert evidence was presented to the court using the hot tub method. Lord Woolman noted that the process was ‘valuable’ and  announced in his judgement that he would use the process in future cases.

Why is it positive in decision making?

The process is seen by many to be an efficient way to hear evidence. The judge asks the witness their own questions directly, helping to focus the minds of all parties on the disputed issue.  This is seen to make it easier for the judge to get to grips with technical issues on their own terms.

As differing positions of witnesses are heard at once instead of complex testimonies weeks apart, experts are able to challenge each other’s testimonies more technically than counsel could in the hot tub and the judge is able to manage the discussion, seeking clarification where necessary.  Each witness must hold their own position in the hot tub and it is more likely that the areas in dispute are thoroughly discussed and understood by the court using this method instead of the traditional adversarial approach.

Why is it negative in decision making?

However, certain issues surrounding the independence of witnesses are called into question.

Several commentators noted that it was likely that the evidence presented at the hot tub was less tested than evidence presented in the traditional way.  There was some concern that, unlike in cross examination, where the rigours of cross-examination are clearly demonstrated to the court, it was possible that some witness statements failed to be scrutinised adequately and so lacked a certain amount of evidential value.

Interestingly, it has been noted that witnesses were not found to have been less impartial in the hot tub.  It appears that although the source of questioning is different, coming from the judge, this has not been seen to affect the objectivity of the witness.

Although the hot tub was agreed to be a more efficient use of court time, it did not necessarily correlate into an overall cost reduction.  It is generally assumed that the hot tub will focus the mind of the court at a faster rate and hearing concurrent evidence will reduce drawn out testimonies, but there has been a divide as to whether or not this will reduce the overall cost to litigants.  Substantial costs are already amassed before matter ends up in court, so although there would be a reduction in the court’s time, preparation and other associated costs still led to significant expenses overall.

Will Hot Tubbing become the norm in Scotland?

In order for hot tubbing to be successful in the Scottish courts, skilled witnesses and judges need to engage fully in the process.  Witnesses that are keen to facilitate debate and who are respectful of others’ opinions will contribute most effectively to the success of the hot tub method.  It will be up to solicitors to choose witnesses who are able to manage discussions but still hold their own view after it has been analysed in the hot tub.  The performance of each witness will be crucial to the value of evidence heard by the judge.

It has been noted that hot tubbing is only beneficial in cases where there is a narrow technical dispute.  Lord Woolman commented in his judgement that in terms of the debate on quantum there was ‘little common ground’ between the witnesses and that the ‘level of detail was too great’.  These factors contributed to a less successful hot tub exercise and shows that only in specific circumstance will this process be advantageous.

Finally, the value of the evidence derived form the hot tub depends on the approach of the judge chairing the session.  It appears that overall the hot tub process is far more time consuming on the part of the judge than hearing testimonies lead by counsel.  Judges will have to do a considerable amount of work behind the scenes to ensure they tease out the correct information.  With time pressures already weighing on the judiciary, this additional burden will require judges to be confident in the merits of the hot tub and prepare substantially for hearings.

Gradually court processes are becoming more streamlined and, as finances run even tighter in the coming years, it is likely that the Scottish courts may employ the hot tub method to a greater extent.   But ultimately the success of the process is likely to depend on the engagement of the judiciary and of the expert witnesses.

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