First-instance decision


In EXP v Barker ([2017] EWCA Civ 63) the Court of Appeal emphasised the importance of independence and objectivity in expert evidence. If there is any conflict of interest, familiarity with a party or apparent interest in the outcome of the proceedings, this should be fully disclosed at the earliest stage. In this case the Court of Appeal upheld the trial judge's decision to take into account the "serious reservations" he had as to the expert's impartiality when considering the weight to afford to his evidence. The Court of Appeal went as far as to say that had the trial judge discounted the expert's evidence in its entirety, it would have supported that view.

The decision serves as a useful reminder of the importance of full and frank disclosure of any connection which might be perceived to affect an expert's evidence.


At first instance, the claimant brought a successful claim for negligence against the defendant for failure to spot an aneurysm in an MRI scan of her brain in 1991. Both parties instructed expert witnesses at trial and their evidence was central to the court's adjudication of the claim.

The defendant's expert had worked in the same hospital as the defendant for seven years. During the trial it became apparent that the defendant and his expert witness had a "lengthy and extensive" relationship which went beyond merely working in the same hospital. The defendant's expert had in fact been his direct mentor for a number of years and had assisted him in promotions, and the two had co-authored a number of journal articles which were absent from their respective CVs submitted to the court in this litigation. Further, it transpired that the defendant had specifically requested that this expert provide evidence for his defence. The connection had not been declared by the defence team or the expert. The trial judge clearly felt that certain steps had been taken to conceal the connection, which caused him serious concern as to the reliability of the expert's evidence and the expert's compliance with his duty to the court.

First-instance decision

The trial judge found that the failure to disclose this close connection was "a very substantial failure indeed", the more so because there had been a specific direction in the case that "experts will, at the time of producing their reports, incorporate details of any employment or activity which raises a possible conflict of interest".

The defence submitted that the individuals' CVs alone should have been sufficient to put the claimant on notice that there was a possible connection and that the onus was on the claimant to investigate the matter. The trial judge dismissed this proposition. The onus was on the defence – in particular, the expert in question, who owed an overriding duty to the court.

The trial judge noted with approval the seven principles applicable to the admissibility of expert evidence in Philipson on Evidence:

"1. It is always desirable that an expert should have no actual or apparent interest in the outcome of the proceedings.

2. The existence of such an interest… does not automatically render the evidence of the proposed expert inadmissible. It is the nature and extent of the interest or connection which matters, not the mere fact of the interest or connection.

3. Where the expert has an interest of one kind or another in the outcome of the case, the question of whether he should be permitted to give evidence should be determined as soon as possible in the course of case management.

4. The decision as to whether an expert should be permitted to give evidence in such circumstances is a matter of fact and degree. The test of apparent bias is not relevant to the question of whether an expert witness should be permitted to give evidence.

5. The questions which have to be determined are whether:

a. the person has relevant expertise; and

b. he is aware of his primary duty to the Court if they give expert evidence, and are willing and able, despite the interest or connection with the litigation or a party thereto, to carry out that duty.

6. The judge will have to weigh the alternative choices open if the expert's evidence is excluded, having regard to the overriding objective of the Civil Procedure Rules.

7. If the expert has an interest which is not sufficient to preclude him from giving evidence the interest may nevertheless affect the weight of his evidence.

Even where the court decides to permit an expert to be called where his independence has been put in issue, the expert may still be cross-examined as to his independence and objectivity."

The trial judge specifically recognised the expert's expertise and experience. However, he considered that the expert was "so compromised" that the decision to admit his evidence at all was "finely balanced", and that as a result the "weight to be accorded to his views must be considerably diminished".

This decision formed the main point on the appeal.


The Court of Appeal held that the trial judge was "fully entitled" to take the view that the evidence must have diminished weight overall when compared to the perceived complete independence of the claimant's expert. The Court of Appeal went a step further and noted that "had [the trial judge] decided to exclude Dr Molyneux's evidence entirely, it would… have been a proper decision". The Court of Appeal went on to emphasise the importance of an expert's independence, stating that:

"our adversarial system depends heavily on the independence of expert witnesses, on the primacy of their duty to the Court over any other loyalty or obligation, and on the rigour with which experts make known any associations or loyalties which might give rise to a conflict."


This case underlines the importance of impartiality and independence in selecting an expert witness. Practitioners should take care to investigate any potential conflicts of interest or perceived connections to either party at the outset. Letters of instruction to an expert should be explicit in the expert's overriding duty to the court. If it is not possible to get a completely independent witness, full and frank disclosure early on in proceedings is crucial; failure to do so – while perhaps innocent – may result in expert evidence being dismissed in its entirety, which may be fatal to a party's case.

While much of this decision turns on the specific facts of the case and the apparent attempts to conceal the connection, it is a useful reminder of the duties of an expert witness and practitioners' concerns when selecting suitable experts. If a connection is unavoidable, this should be disclosed to the other party as soon as practicable and discussed at the case management stage.

For further information on this topic please contact Fiona Rafla at RPC by telephone (+44 20 3060 6000) or email ([email protected]). The RPC website can be accessed at