Evidence which consists of a witness’ opinion is generally inadmissible in court proceedings.
The principal exception to this is expert evidence. In technical matters, the assistance of an expert is typically required for the court to be able to resolve the proceedings. Expert evidence is only admissible with the permission of the court.
Expert witnesses should be independent of the parties and of the dispute. This is to avoid any conflict of interest arising which may impact on the expert’s actual or perceived objectivity in the performance of his duties to the court.
If an expert has an interest in the result of the proceedings, it does not automatically mean that his evidence is inadmissible. The court has to decide whether the expert is able to carry out his duty to the court, notwithstanding the existence of an interest or connection with the dispute or one of the parties.
In EXP v Charles Simon Barker  EWHC 1289 (QB), it only emerged in cross-examination at the trial that there was a connection between the Defendant and his expert witness that the Judge called “lengthy and extensive”. The case concerned a claim in negligence against a consultant radiologist for failing to identify and report the presence of an aneurysm following an MRI brain scan. It came to light that:
- The expert had trained the Defendant during his seven years of specialist radiology training, and in particular had trained him for two and a half years as a registrar and senior registrar in neuroradiology, including the particular area of interventional radiology in which the expert specialised and in which the Defendant had a special interest.
- They had worked together closely over a substantial period.
- They had written together a paper for an international symposium on radiology.
- They might have co-operated on other papers which the expert could no longer specifically recall.
- The expert helped the Defendant to obtain two foreign fellowships. The expert had guided and inspired the Defendant’s practice, and had helped him become a consultant.
- They had been officers together on the committee of the British Society of Radiologists.
The Judge rejected a request from the Claimant that the evidence of the Defendant’s expert witness should be excluded entirely, but commented that: “…I must bear powerfully in mind, when I assess the weight that I should give to the evidence, the reservations that I retain about [the expert’s] independence and objectivity in the case”.
With a devastating effect on the Defendant’s case, the Judge’s confidence in the expert’s independence and objectivity was “very substantially undermined”.
The judgment identifies that the issue of independence should have been explored before the trial began. It was both “fair and economical” that the Defendant disclosed the details of the connection between him and his expert. The Judge said that the burden was “fairly and squarely” on the Defendant and in particular on the expert witness “to state frankly, with adequate particulars, the nature and extent of any connection between them”. The absence of such disclosure was described by the Judge as a “very substantial failure indeed” both on the part of the defence more generally, and also specifically on the part of the expert himself.
Particularly as this was a clinical negligence claim where expert evidence is often determinative of the outcome of a case, it is surprising that an expert was put forward who had such extensive professional associations with the Defendant thereby opening up the objectivity of the expert to challenge.
Instances of such close connections between a party and its expert are far from usual, but the case is a warning (if one be needed) to litigants and their advisers of the need to ensure that the expert evidence on which they rely is unimpeachable on grounds of propriety. Doing otherwise can result in a highly detrimental (and expensive) own goal.
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