For most clients and for many lawyers the role of an expert witness is to support their side's case. But courts are losing patience with this approach and consider it to be legally and professionally flawed.
The problems start with three different roles the expert may be required to play. As a negotiator he is entitled to be partisan; as an advocate (in arbitration and other tribunals where he has rights of audience) his role is one of persuasion with no obligation to put forward a balanced case; but as an expert witness his role is to give his honest opinion "uninfluenced by the exigencies of litigation".
The courts have been unimpressed by the tendency of expert witnesses to "descend into the arena" - EG Wallshire v Aarons (1989). In Autospin (Oilseals) v Beehive Spinning TLR 9/8/95, it was noted that the weight given to experts' evidence carried with it a responsibility to approach the task seriously and an expert should not be surprised if the court expressed strong disapproval if this was not done. In that case the expert supported a claim that the plaintiff's coding system was unique. However, it became clear that others used the system, that the expert was unaware of what systems were used and had made no effort to find out.
The courts have been willing to uphold subpoenas against expert witnesses where there is evidence the expert may have expressed different views before. "If a witness were to have expressed himself in a materially different sense when acting for different sides that would be a factor which should be brought out in the interests of the litigants involved and in the public interest" - London & Leeds v Paribas Nos 2 and 3 (1995).
There is a strong argument that a degree of partiality is helpful to the parties or the tribunal. Expert evidence needs to be tested either in negotiations or in cross-examination. In Holding & Management v PHIT and ors, the landlords for remedial works were challenged by the tenants and the parties settled on a reduced scheme as proposed in the tenant's expert's report. Would a court-appointed expert have had any incentive to explore more cost effective solutions, as the tenant's expert did?
The key to good expert evidence is neither its support for the client's cause nor its independence from the exigencies of litigation. Instead the expert should:
have the necessary expertise, be it in letters after their name or in the field or both;
have the forensic ability to understand the issue in dispute and how their expertise relates to it;
be able to set out his conclusions and reasons and answer questions on them with consistency and coherence;
be able to present conclusions with persuasive, but dispassionate conviction.