In Hayden v Maidstone & Tunbridge Wells NHS Trust  EWHC 1121 (QB) the judge was faced with an application made at the very last minute by the defendants for permission to rely on surveillance evidence recently obtained by them and which they considered undermined the claimant’s case. The possible benefit of such evidence had been ‘sign-posted’ by the defendants’ pain expert, and he had been asked to review the edited film once it was obtained. He found this film supportive of his criticism of the claimant’s case.
One of the perhaps not very attractive arguments put forward by the defendants as to why, despite the last minute disclosure, the surveillance evidence should be admitted was that it would be difficult for an expert who has seen the surveillance evidence to put it out of his mind and to make no reference to it when he came to give evidence and to be cross-examined. The judge did not consider that that could be a reason for a court to feel obliged to admit the evidence.
‘Experts are familiar with the need not to refer to the content of any “without prejudice” discussions with their counterparts and the same applies, albeit doubtless with less familiarity, to [the parties themselves] who have to be advised by their lawyers not to make reference when giving their evidence to what was said during “without prejudice” negotiations.’ (para 40)
So experts can be expected, when giving evidence of their opinion, to put out of their minds material evidence of which they have knowledge. The judge continued:
‘When, inadvertently, some forbidden material “slips out” during the course of giving evidence, all judges are familiar with the need simply to put such material out of their mind.’
That is part of a judge’s ‘training’. But what if, despite being made aware of the need to ‘forget the evidence’, the expert still makes reference to it in the course of evidence?
‘Where some obviously deliberate attempt is made to refer to such material, it will weigh heavily in the evaluation of the witness who makes such an attempt.’
So the witness is likely to lose credibility with the court if the genie is not placed firmly back in the bottle while giving evidence.
In Hayden the judge therefore found that the difficulty of ‘forgetting’ that which was known was not a ‘determinative consideration’ in the exercise of his discretion as to whether or not the evidence should be admitted. Indeed the judge found this argument ‘deeply unattractive’. (para 41)
Given an expert’s duties and the requirements of the Civil Procedure Rules, the position could become somewhat more complicated, if for example the expert saw surveillance evidence, found it material, and altered his or her opinion. The expert’s report must state the substance of all material instructions, whether written or oral, on the basis of which the report was written (CPR 35.10(3)); must contain a statement setting out the substance of all facts and instructions which are material to the opinions expressed in the report or upon which those opinions are based (35 PD 3.2(3)); and if, after producing a report, an expert’s view changes on any material matter, such change of view should be communicated to all the parties without delay, and when appropriate to the court (35 PD 2.5).
An expert witness must understand that, in certain circumstances, there are some matters which may be within the expert’s knowledge which may not be relied upon in the course of a trial – facts which the expert is under a duty to forget for the purposes of the trial. Thankfully such instances will be out of the usual, and these are matters on which the expert must seek advice from the instructing lawyers.
In fact, in Hayden, the judge admitted the surveillance evidence despite the defendants’ dilatory actions although ‘with considerable misgivings’. By the time that the application (to admit the surveillance evidence) was finally to be determined the claimant and one of her expert’s had reviewed the edited film, and the judge stated that he was influenced in his decision ‘by the fact that the claimant and one of her principal medical experts have been able to answer (… at least at face value) the new material and [the defendants’ expert’s] analysis of it in a strong fashion.’ Moving from the Arabian Nights to a sporting analogy he concluded that ‘the playing field has, in my view, remained level.’ (para 56)