In Hayden v Maidstone & Tunbridge Wells NHS Trust [2016] 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)

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It is useful to keep well in mind the 2 roles that an expert may have as a court expert and the 2 separate, but often overlapping, reasons why the expert may have been instructed.  The recent Supreme Court decision in Kennedy v Cordia (Services) LLP [2016] UKSC 6 was concerned with the evidence of an engineer in relation to a slipping case and although dealing with an appeal from Scotland, the Court’s observations are equally applicable to England and Wales.

Like any other witness the expert may be an expert of fact giving evidence of what he or she observed, so long as it is relevant to a fact in issue in the case.  So a medical expert may give evidence of an examination of the claimant, or the appearance of the claimant on arriving or leaving the consulting room. An engineer may provide measurements of a machine or location.

As a skilled witness, an expert ‘may also give evidence based on his or her knowledge and experience of a subject matter, drawing on the work of others, such as the findings of published research or the pooled knowledge of a team of people with whom he or she works.’  A medical expert may therefore, for example, give evidence as to how an organ functions and the potential impact on the organ of disease.  An engineer may describe how a machine is configured or works.  This is not opinion evidence, but for such evidence to be admissible from the witness, the same rules that govern admissibility of expert opinion evidence also apply.  Therefore to be permitted to give this evidence, ‘the skilled witness must set out his qualifications, by training and experience, to give expert evidence and also say from where he has obtained information if it is not based on his own observations and experience.’

This expert factual evidence may be given by itself or in combination with opinion evidence.  Opinion evidence, in contrast to expert factual evidence, will address, for example in medical expert evidence, prognosis, causation or standard of care, and in engineering evidence measures which might reasonably have been taken to avoid an accident.

Whether giving skilled evidence of fact or expert opinion the admissibility of the skilled evidence is governed by the same four considerations:

1. Will the evidence assist the court in its task?
2. Does the witness have the necessary knowledge and experience?
3. Is the witness impartial in the presentation and assessment of the evidence?
4. Is there a reliable body of knowledge or experience to underpin the expert’s evidence?

What is essential is that the expert explains the basis of his or her evidence when it is not personal observation or sensation.  ‘Mere assertion carries little weight.’  Quoting from a South African case the Supreme Court stated:

‘Except possibly where it is not controverted, an expert’s bald statement of his opinion is not of any real assistance.  Proper evaluation of the opinion can only be undertaken if the process of reasoning which led to the conclusion, including the premises from which the reasoning proceeds, are disclosed by the expert.’

And quoting from a Scottish case, the Supreme Court stated:

‘As with judicial or other opinions, what carries weight is the reasoning, not the conclusion.’

The expert in writing a court report should bear these points well in mind.  When giving evidence of factual matters known only as a consequence of having the particular skills for which reason the expert has been instructed, and even more so when giving an opinion, in addition to providing the appropriate expert credentials to justify the status as the appropriate expert, the expert must provide clear statements as to the reasoning process which led to each conclusion reached.  It is the reasoning process as much as, and often more than, the conclusion which carries weight with the judge.

Kennedy v Cordia also provides very useful guidance as to those matters which it is appropriate for a health and safety expert to address in an expert report and the line between what it is appropriate for the expert to address in opinion evidence and for the judge to resolve.

Finally the Supreme Court reminds lawyers instructing experts that it is their duty to assess whether the skilled witness has the necessary expertise and to ensure that the skilled witness is aware of all of the duties imposed on an expert witness.

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