Expert witness

Category: Claims and policy principles · Reviewed by the Apex broking team · Last reviewed 2026-08-22 · ~5 min read

Definition and duty

An expert witness is a person permitted to give opinion evidence because of specialist knowledge — a surveyor on valuation, an engineer on causation, an accountant on quantum, a clinician on prognosis. The governing rule in England and Wales is CPR Part 35. Rule 35.3 states that “it is the duty of experts to help the court on matters within their expertise” and that “this duty overrides any obligation to the person from whom experts have received instructions or by whom they are paid”. Rule 35.4 makes expert evidence permissive rather than automatic: “no party may call an expert or put in evidence an expert’s report without the court’s permission”. Rule 35.10 requires the report to state the substance of all material instructions, written or oral, on which it was written.

The removal of immunity: Jones v Kaney

Expert witnesses were long protected by an immunity from suit in respect of their participation in proceedings. In Jones v Kaney [2011] UKSC 13, decided on 30 March 2011, the Supreme Court abolished it. By a majority of five to two — Lord Hope and Lady Hale dissenting — the Court held that an expert retained by a party is no longer immune from a claim in negligence or breach of contract by that party arising from the way the expert performed the retainer, including evidence given and statements made in anticipation of giving evidence. The case concerned a psychologist who signed a joint statement that undermined her own client’s claim. The decision was confined to claims by the instructing party; it did not create a route for an opposing litigant to sue the other side’s expert, and the absolute privilege that protects witnesses against defamation claims was not disturbed.

What that means for insurance

Before 2011 the immunity was, in effect, free cover. After it, an expert’s exposure to its own client is an ordinary professional liability, and professional indemnity insurance is the mechanism that answers it. Two questions decide whether an expert is actually insured for it. Does the schedule’s definition of Business or Professional Services include expert witness and litigation support work? Many professionals do expert work occasionally, under a description written for their day job, and find it is not there. And does the policy carry a sufficient limit, given that defence costs on most PI wordings erode the limit — see defence costs inside vs outside the limit. A dedicated approach is set out under expert witness PI cover.

Where the exposure actually arises

Claims against experts cluster in predictable places: a joint statement signed without proper thought, as in Jones v Kaney itself; a report that goes beyond the expert’s field; missed deadlines that cost a party its evidence; failure to state material instructions or to disclose a conflict; and opinions that shift materially between report and cross-examination. Costs sanctions and, in serious cases, wasted costs applications are additional exposures that a policy may or may not treat as a covered “claim”.

Experts on the other side of the relationship

Experts also feature in insurance claims as the insurer’s tool. In a defended liability claim the panel solicitor will instruct experts on liability, causation and quantum, and the insured’s cooperation obligations extend to giving those experts access and information — see defence panel solicitor and claims cooperation clause. The insured should understand that these experts are instructed for the litigation, that their reports may be disclosable, and that candour with them matters as much as candour with the lawyers.

Practical points for anyone taking expert instructions

Confirm the retainer in writing, including scope, fees and the Part 35 duty. Check the instruction is within your actual expertise and say so if any part is not. Record material instructions as they are given. Treat a joint statement as a substantive step requiring preparation, not a formality. Notify your insurers of any criticism from a court, any wasted costs application and any complaint from an instructing solicitor as a circumstance — see circumstance notification.

Why it matters

Expert work is often a small part of a professional’s income and a disproportionate part of their risk. The combination of a duty that overrides the paying client, a report that will be tested in public, and no immunity from the client’s own claim, makes it a distinct exposure that should be underwritten deliberately rather than assumed.

Frequently asked questions

Can an expert witness be sued for a negligent report?

Yes, by the party who instructed them. In Jones v Kaney [2011] UKSC 13 the Supreme Court abolished the immunity from suit that expert witnesses had enjoyed, by a majority of five to two, in relation to claims by the instructing party.

Does my ordinary professional indemnity policy cover expert witness work?

Only if the schedule’s Business or Professional Services description covers it. Expert and litigation support work is frequently omitted from descriptions written for a professional’s main practice, so it should be confirmed with the broker before instructions are accepted.

Who does an expert owe their duty to?

The court. CPR 35.3 provides that the duty to help the court on matters within the expert’s expertise overrides any obligation to the person instructing or paying them.

Related entries

• Expert witness PI cover
• Defence panel solicitor
• Defence costs inside vs outside the limit
• Definition of Business
• Professional indemnity insurance

This entry is part of the Apex Insurance Wiki. Last reviewed 2026-08-22. Next review: 2027-02-22. It is general insurance information, not legal advice, and it describes UK market practice and law as at August 2026.

Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority (FRN 724952). This page is general information, not advice on a specific policy.