The duty an expert witness owes the court is well documented in case law and the Civil Procedure Rules (CPR). CPR 35 sets out the expert’s overriding duty to the court – it is the duty of an expert to help the court on the matters within their expertise and this overrides any obligation to the person who has instructed him or by whom he is paid.

Previously, where an expert witness had breached this duty, they could be found guilty of contempt or, at its most extreme, perjury.