Expert evidence

Introduction to the use of expert evidence

General rule

At common law there is a general rule that witnesses must state facts not opinions. There are effectively two exceptions to this general rule: certain types of evidence given by non-expert witnesses and the evidence given by expert witnesses

Non-expert witnesses

A non-expert witness is allowed to express an opinion or impression where the facts perceived are too complicated or too evanescent in their nature to be recollected or separately and distinctly narrated. Some examples of matters on which a non-expert witness may state an opinion as a compendious way of stating facts are:

  • Estimations of speed and distance;
  • The identity of persons or articles;
  • The state of the weather;
  • The condition of articles;
  • The age of persons or articles 

Expert witnesses

An expert witness may rely on published and unpublished material in reaching conclusions, draw on his or her own experience and that of colleagues, and may refer to research papers, learned articles and letters during the course of giving testimony, such documents being themselves admitted in evidence and supporting any inferences which can fairly be drawn from them.

Admissibility of expert evidence

When will expert evidence be admissible?

The following conditions must be satisfied:

  • The matter must call for expertise; the inquiry has to be into a matter of art or science which is likely to be outside the experience and knowledge of the tribunal of fact. Expert help is therefore unnecessary on matters relating to normal human nature and behaviour.
  • The evidence must be helpful to the court in arriving at its conclusion;
  • There must be body of expertise in the area in question;
  • The particular witness must be suitably qualified as an expert in the particular field of knowledge; the question is whether the witness has sufficient skill and knowledge in relation to the field in question. There is no absolute requirement that the witness be professionally qualified, there being several areas where expertise is obtained through experience rather than study.
  • Permission to rely on the expert evidence must be obtained from the court.

Conflicts with expert evidence

Where there is a conflict between an expert and lay witnesses, generally the judge should refuse to accept the lay evidence in preference to uncontradicted expert evidence. However, the judge is not obliged to accept expert evidence if there are sufficient grounds for rejecting it, such as where it does not speak to a relevant issue, or where the judge does not believe the expert or is otherwise unconvinced by it.

Obtaining facilities for inspection by experts

When will a stay of proceedings being ordered?

The principle laid down by Lord Denning MR was that a stay would be ordered if it was just and reasonable to do so. Put another way, the court would order a stay if the conduct of the claimant in refusing a reasonable request was such as to prevent the just determination of the cause. Thus the test is twofold:

  1. Is it reasonable to order an examination? And if so,
  2. Is the claimant’s conduct in refusing an examination such as to prevent the just determination of the cause?

However, whether or not a stay is granted is entirely within the discretion of the court, and it will only grant a stay if the applicant satisfies it that a stay is required in the interests of justice. The facts of each individual case, and the parties’ reasons for asking for, or resisting, the proposed medical examination, are all matters which must be taken into consideration; and each party is under a duty to provide the court with the necessary material to enable the proper exercise of its discretion. 

Legal professional privilege

Experts’ reports, whether medical or non-medical, and whether obtained by the claimant or the defendant, if made for the purpose of pending or contemplated litigation, are privileged. Therefore, the exchange of experts’ reports cannot, properly be made the subject of an interim order.

Directions regarding expert evidence

Generally, expert evidence is not allowed in small claims track cases, so the following is principally aimed at fast track and multi-track cases. Experts should be served with a copy of any order containing directions which may affect them. When considering expert directions, the starting point is that no party may call an expert or put in evidence an expert’s report without the court’s permission. In the absence of a direction, therefore, expert evidence is inadmissible. In deciding whether to grant permission, and if so to what extent, the court will seek to restrict expert evidence to that which is reasonably required to resolve the proceedings.

Traditionally, if expert evidence was permitted, both parties would instruct competing experts. This is still possible, and the most likely approach in multi-track cases. Recently, there has been a move towards the joint instruction of a mutually acceptable expert who it is intended will produce a report which is objective and not biased towards either side. This is in fact the favoured approach in fast track cases.

Joint instruction of experts

Where two or more parties wish to submit expert evidence on a particular issue, the court may direct that the evidence on that issue is to be given by one expert only. If the court makes such a direction, unless the parties agree on the expert to be instructed, the court may select an expert from a list submitted by the parties, or direct how the expert should be selected. Once selected, each instructing party may give instructions to the expert, sending a copy to the other instructing parties.