Expert Evidence

The general rule is that witnesses in court proceedings must state the relevant facts as they know them, and not opinions. Like all rules, there are exceptions, such as the evidence given by expert witnesses

What is an expert witness?

An expert witness is a witness who is called upon to give evidence because of their expertise and experience in their area of work or interest. For example, a doctor giving expert medical evidence; a forensic accountant giving expert evidence about a financial trail; and a car engineer providing evidence about the mechanics of a vehicle.

An expert witness may rely on published and unpublished material in reaching their conclusions; draw on their own experience and expertise; and may refer to research papers, articles and letters during the course of giving testimony. Those documents themselves would probably be admitted in evidence to support their evidence, and any inferences which can fairly be drawn from them.

Expert witnesses are bound by the rules of the Court (the Civil Procedure Rules) when preparing and giving their evidence.

Admissibility of expert evidence

When will expert evidence be admissible?

For expert evidence to be admissible in court, the following conditions must be satisfied:

  • The matter must require 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. The expert witness does not have to be professionally qualified: there are several areas where expertise is obtained through experience rather than study – for example, through a hobby
  • Permission to rely on the expert evidence must be obtained from the court

What if there are conflicts between the evidence of an expert and another witness’s evidence?

Where there is a conflict between an expert and lay witnesses, the judge will usually 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.

What is legal professional privilege and how is this relevant?

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’. This means they do not have to be disclosed to the other side – until the court gives permission by way of directions or an order. However, the rules of privilege and disclosure are complex and legal advice should be taken if necessary.

Directions regarding expert evidence

Generally, expert evidence is not allowed (or necessary) in small claims track cases, so these rules are principally relevant to 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.

Joint instruction of experts

Traditionally, if expert evidence was permitted, both parties would instruct their own expert witness. This is still common, and the most likely approach in multi-track cases.

Recently, however, 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 far more cost effective where it is an acceptable course of action to the court and the parties, and is now the favoured approach in fast track cases in particular.

So 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 a joint 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.

The expert witness must then work closely to those instructions, taking into account the available evidence and the circumstances of the case, and present their objective expert report and evidence to the parties, and the court if required.

Article written by...
Lucy Trevelyan LLB
Lucy Trevelyan LLB

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Lucy graduated in law from the University of Greenwich, and is also an NCTJ trained journalist. A legal writer and editor with over 20 years' experience writing about the law.