Evaluating the independence of an expert witness: lessons from The Ikarian Reefer

The principle of expert witness independence

In civil litigation in England and Wales, the independence of an expert witness is governed by the principles established in National Justice Compania Naviera SA v Prudential Assurance Co Ltd (The Ikarian Reefer) [1993] and operationalised under CPR Part 35. The expert’s primary duty is to the court, as set out in CPR 35.3, which overrides any obligation to the party instructing them. This duty is essential to the admissibility and weight of the evidence provided.

An expert’s evidence should be the independent product of the expert, uninfluenced by the pressures of litigation. Where an expert fails to demonstrate this neutrality, the reliability of their opinion on matters such as breach of duty or causation may be scrutinised, potentially limiting the weight the court assigns to that evidence.

Evidence establishment and the duty to the court

Expert evidence is intended to assist the court on matters outside the knowledge of the judge. Under CPR 35.10, the report must clearly distinguish between facts relied upon—such as medical records or imaging—and the expert’s opinion. Where the evidence is incomplete, or the opinion relies on contested factual premises, the report should state these limitations. An expert should remain prepared to modify their opinion if the facts, or the evidence provided during the litigation, indicate that an initial assessment is no longer supported.

• Experts must state the facts or assumptions on which their opinions are based.
• Opinions must be restricted to matters within the expert’s own field of expertise.
• Where there is a range of opinion on a matter, the expert should summarise that range and explain the basis for their particular view.
• If an expert identifies that their opinion is incomplete without further information, they must notify the instructing party to consider whether to seek directions under CPR 35.14.

Discipline boundaries

Independence requires an expert to recognise the limits of their discipline. A common issue arises when an expert ventures beyond their professional remit. Where an opinion rests on facts that fall outside the expert’s specific expertise, the report should acknowledge this or rely on a report from a more appropriately qualified specialist. Failing to recognise these boundaries can undermine the perceived objectivity of the expert.

Procedural safeguards in England and Wales

The rules provide mechanisms to ensure that independence is maintained. Under Practice Direction 35, experts are encouraged to narrow the issues in dispute. When two or more experts are instructed, the court may direct them to participate in discussions and produce a joint statement under CPR 35.12. This process is intended to foster professional dialogue to identify areas of agreement and disagreement. It is a fundamental breach of duty for an expert to allow their contribution to a joint statement to be dictated by the legal team.

In contrast, the use of a single joint expert under CPR 35.7 involves one expert instructed by multiple parties. A single joint expert does not participate in a joint statement process with another expert, as there is no second expert in that discipline. In all cases, whether acting as a single joint expert or a party-appointed expert, the duty to the court remains primary. An adverse clinical outcome alone is not proof of breach; the expert must address the established legal standards for negligence, such as the Bolam and Bolitho tests, rather than simply identifying that a poor outcome occurred.