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Expert witnesses

What is an expert witness?

An expert witness (also often referred to as a professional witness) is someone with knowledge or experience of a particular field or discipline beyond that to be expected of a layman. An expert witness makes this knowledge and experience available to a court to help it understand the issues of a case and thereby reach a sound and just decision.

What is expert evidence?

The fundamental characteristic of expert evidence is that it is opinion evidence that is independent, objective and unbiased.  To be of maximum assistance to a court, expert evidence must also provide as much detail as is necessary to convince the judge that the expert's opinions are well founded. It follows, then, that it will often include:

  • factual evidence obtained by the witness which requires expertise in its interpretation and presentation
  • factual evidence which, while it may not require expertise for its understanding, is linked to evidence that does
  • explanations of technical terms or topics
  • hearsay evidence of a specialist nature, e.g. as to the consensus of medical opinion on the causation of particular symptoms or conditions

as well as

  • opinions based on facts adduced in the case.

When are expert witnesses needed?

Expert evidence is most commonly sought in disputes requiring detailed scientific or technical knowledge from expert witnesses.

Duties of an expert witness

The primary duty of an expert witness is to the court - to be truthful as to fact, thorough in technical reasoning, honest as to opinion and complete in coverage of relevant matters. This applies to written reports as much as oral evidence, and regardless of whether the witness is on oath.

At the same time, when accepting instructions the expert assumes a responsibility to the client to exercise due care with regard to the investigations he carries out and to provide opinion evidence that is soundly based. This requires that the expert undertakes only those tasks he is competent to carry out and gives only those opinions he is competent to provide.

To fulfil these duties adequately it is, of course, vital that the expert should also have kept up to date with current thinking and developments in his field.

In addition, the expert must treat as confidential the identity of the client and any information about him or her acquired in the course of investigations, unless their disclosure is required by law or has been authorised by the client.

Finally, anyone accepting instructions to act as an expert witness should ensure that he or she is familiar with the provisions of Part 35 of the Civil Procedure Rules and the associated Practice Direction, and the CJC Experts Protocol. An expert should be ever-mindful of the potential consequences for the client of a failure on the expert's part to observe their requirements. The provisions governing experts in criminal cases are contained in Part 33 of the Criminal Procedure Rules.

An expert witness should have

  • a sound knowledge of the subject matter in dispute, and, usually, practical experience of it
  • the powers of analytical reasoning required to fulfil his assignment
  • the ability to communicate findings and opinions clearly, concisely and in terms adapted to the tribunal before which evidence is being given
  • the flexibility of mind to modify opinions in the light of fresh evidence or counter-arguments
  • the ability to 'think on one's feet', so necessary in coping with cross-examination, and
  • a demeanour that is likely to inspire confidence, particularly in court appearances.

An expert witness as an adviser

An advisory role is enormously extended if it should be decided to proceed to trial. The expert may then be expected to advise on:

  • the technical matters adduced in the statement of case
  • the technical content of requests for further particulars (or the responses to such requests)
  • the technical significance of documents disclosed by the opposing side.

as well as to produce his own report for use in court.

Furthermore, after reports have been exchanged, the expert will probably be asked for an assessment of the report prepared by the expert for the opposing side.

During the hearing of a case on the multi-track an expert will not only have to face cross-examination on his own evidence, but be on hand to advise counsel about weaknesses to be probed in that of the opposing side's expert. Finally, the expert may be required to provide further technical support should the case go to appeal.

An expert witness can have several distinct roles to play in litigation, these roles will overlap in time and they may extend over the duration of a case, from inception to appeal. Being an expert witness is not just a case of writing reports- it can involve much else besides.

Expenses incurred as an expert witness

Expenses will be paid for all witnesses attending trial, for those giving expert evidence please see below for payment structures.