Expert Witnesses PI Insurance UK 2026

A consulting structural engineer with twenty-five years of expert witness work — single joint expert in three High Court cases at any one time, regular instruction by both claimant and defendant solicitors in subsidence and structural defect claims, members of the Academy of Experts and the Expert Witness Institute — is instructed in a Technology and Construction Court case turning on the cause of progressive structural failure in a 1990s-built apartment block. The expert produces a 240-page report. Three weeks before trial the opposing expert's joint statement under CPR 35.12 highlights two foundation-related calculations that the expert had based on borehole data that, on closer reading, was from a different site. The expert acknowledges the error in cross-examination. The case settles within a week on terms materially worse to the instructing party than the position assumed before disclosure of the error. The instructing party sues the expert for £1.4m representing the differential between the settled position and what the case was reasonably worth had the error not been made. The expert's PI sits at £2m each-and-every. The wording carries an expert witness extension. The instructing party's claim is for negligence in the preparation of the report. Defence rests on whether the policy responds to the act of giving expert evidence under CPR Part 35, on the standard of care a reasonably competent expert would have applied, and on whether the error materially altered the case outcome.

That scenario was a clean impossibility before 30 March 2011. On that date the Supreme Court in Jones v Kaney [2011] UKSC 13 abolished the long-standing immunity from suit that expert witnesses had enjoyed in respect of their conduct as experts. The expert can now be sued — by the party who instructed them — for negligence in the preparation of expert evidence. The expert's exposure flows from CPR Part 35, from the contractual instruction, and from the tort of negligence. The expert's PI cover is the protection against the consequences.

This guide is written for individual expert witnesses, partners in firms providing expert witness work as part of a broader practice, and companies built specifically around expert witness work. It covers the legal framework, the CPR duties, the recurring claim types, the wording questions that matter, and the practical position on AI in expert work which has moved from theoretical concern to live underwriting issue over the last twenty-four months.

The legal framework — CPR Part 35

The Civil Procedure Rules Part 35 governs the conduct of expert witnesses in civil proceedings in England and Wales. Three rules carry most of the practical weight.

CPR 35.3 sets the expert's overriding duty:

"It is the duty of experts to help the court on matters within their expertise. This duty overrides any obligation to the person from whom experts have received instructions or by whom they are paid."

The overriding duty to the court is the single most important framing concept in expert witness work. The expert is paid by the instructing party but the duty runs to the court. The Practice Direction to CPR Part 35 (PD35) sets out the form and content of expert reports and the requirements for the expert's declaration that the report complies with the duty.

CPR 35.7 permits the court to direct that expert evidence be given by a single joint expert (SJE) where two or more parties wish to submit expert evidence on a particular issue. The SJE is jointly instructed by all the parties and owes the duty to all of them. The SJE position is increasingly common in family proceedings, lower-value commercial cases, and any case where the court takes the view that the issue does not warrant duelling experts.

CPR 35.12 requires experts to meet, identify the issues, and prepare a joint statement of the points on which they agree and the points on which they disagree. The joint statement is the moment in many cases where errors, methodological gaps and confidentiality issues come to light.

The Practice Direction (Pre-Action Conduct and Protocols) and various subject-specific pre-action protocols require parties to consider expert evidence before issuing proceedings. Experts instructed at the pre-action stage are subject to the same Part 35 framework if the matter proceeds.

Jones v Kaney and the end of immunity

Before 2011, expert witnesses enjoyed a long-standing immunity from suit in respect of their conduct as experts, derived from Watson v M'Ewan [1905] AC 480 and confirmed in Stanton v Callaghan [2000] 1 QB 75. The rationale was the public interest in experts being free to give honest evidence without fear of vexatious litigation by dissatisfied parties.

The Supreme Court in Jones v Kaney abolished the immunity by a 5-2 majority. Lord Phillips, giving the leading judgment, held that the immunity was an anomaly inconsistent with the general principle that wrongs should have remedies. The expert remains protected by absolute privilege from defamation claims arising from evidence given in court, and from claims by adverse parties for negligence — the immunity is abolished only as between the expert and the instructing party.

The post-Kaney position is straightforward. An expert who provides a negligent expert report or negligent expert evidence to the instructing party can be sued by that party for the consequences. The expert remains protected against claims by the adverse party. The standard of care is the ordinary professional standard — that of a reasonably competent expert in the relevant field.

The practical consequence has been a steady rise in expert E&O claims since 2011. Numbers remain modest compared to mainstream professional negligence, but the average claim is materially larger than the average professional negligence claim because the expert's error has typically changed the outcome of substantive litigation.

The contractual structure

The expert is instructed under a contract of services with the instructing solicitor or party. The terms of the instruction govern the scope, the fee, the deliverables and (often) the limitations on liability. A well-drafted expert instruction will:

Define the scope of the opinion — the issues to be addressed, the documents to be reviewed, the assumptions on which the opinion proceeds
Identify the form of the deliverable — preliminary advisory note, formal report, joint statement participation, oral evidence at trial
Set the fee — hourly, capped, fixed by stage
Set a cap on liability, typically aligned to the fee multiplied by some factor or to a stated monetary cap
Include a confidentiality clause and a position on conflicts
Reserve the expert's overriding duty to the court under CPR 35.3

Liability caps in expert engagement letters are increasingly common and increasingly accepted by instructing solicitors, particularly where the expert is an individual or a small specialist practice. The cap protects the expert from open-ended exposure to litigation outcomes that may run into multiples of the expert's fee.

The cap does not, however, limit the expert's exposure to wasted costs orders under section 51(6) of the Senior Courts Act 1981, which courts can make directly against an expert in circumstances of improper, unreasonable or negligent conduct of the proceedings. Wasted costs orders are rare but possible and sit outside the contractual cap with the instructing party.

Common claim types

Expert witness E&O claims cluster around a small set of recurring fact patterns.

Methodological error

The expert has applied a methodology that the court, on hearing the evidence, finds inadequate or incorrect. The instructing party loses on the issue and brings a claim against the expert. Defence rests on whether the methodology was within the range of reasonable expert opinion at the time the report was prepared — the Bolam / Bolitho standard adapted to expert opinion.

Factual error in the report

The expert has misread, misunderstood or overlooked material in the disclosed documents. The error comes to light in joint statement, cross-examination or at trial. The instructing party brings a claim for the consequences. Defence rests on the expert's documented review process, the scope of the instruction, and whether the error materially altered the outcome.

Missed disclosure or late identification of issues

The expert was given the full disclosure but failed to identify an issue that a reasonably competent expert would have identified, or the issue was identified too late for the instructing party to deal with it. Both fact patterns generate claims.

Conflict of interest

The expert had a conflict — undisclosed relationship with one of the parties, prior involvement on related matters, financial interest — that came to light during the proceedings. The expert's evidence is excluded or given reduced weight, the instructing party loses or settles unfavourably, the expert is sued. Defence rests on the conflict-clearance process and the documented enquiry at instruction.

Breach of confidentiality

The expert disclosed or used material from one instruction in connection with another. Common where the expert practices in a narrow specialism with overlapping party populations. The remedy is typically an injunction plus damages.

Defamation claim by an adverse party

The expert's report contains criticism of an adverse party, the criticism is repeated outside the privileged context (in correspondence with non-parties, in a published article, in a CV listing), the adverse party brings a defamation claim. The expert's absolute privilege protects evidence given in court but not extra-judicial repetition.

Wasted costs order

A direct order under section 51(6) of the Senior Courts Act 1981. Rare. The threshold is high — improper, unreasonable or negligent conduct of the proceedings. The expert pays a defined sum direct to the parties for costs wasted.

Tribunal and arbitration work

Expert work in arbitration, expert determination, adjudication, regulatory tribunals and family court proceedings sits under different procedural rules but the substantive liability position post-Kaney is the same. The cover wording must capture all the forums the expert works in.

The wording — what to read

Most expert witness PI sits inside the wider professional liability of the expert's underlying profession — surveyor, engineer, accountant, doctor, solicitor — and the expert witness exposure is covered by extension. A smaller market of standalone expert witness PI exists, principally for full-time experts or expert witness companies.

The wording questions to read carefully:

Express expert witness extension. The wording should expressly cover the firm's or individual's expert witness activity. Some standard professional PI wordings draw the cover around "the firm's professional services" and treat expert witness work as included by inference. The express extension removes the ambiguity.

Civil liability basis. Civil liability is the standard. Narrower triggers — "negligent breach of professional duty" — may not capture all the contractual and statutory bases on which expert claims now proceed.

Scope — court, tribunal, arbitration, adjudication, expert determination. The wording should cover all the forums the expert works in. Family court work, criminal court work (defence-instructed and prosecution-instructed), regulatory tribunals (FCA, GMC, SRA, RICS, ICAEW, ARB), and international arbitration are common scope questions.

Single joint expert work. Some wordings carry SJE-specific provisions, recognising that the SJE owes duties to multiple instructing parties. The wording should not carve out SJE work.

Wasted costs orders. Cover for section 51 wasted costs orders varies. Some wordings cover them up to a sub-limit; some exclude them. Experts at the front line of the SJE family court population in particular should know the position.

Defamation cover. Some wordings carry defamation as a named extension. Worth having for active experts and expert authors.

Cover for criticism by an adverse party. Where an adverse party criticises the expert's conduct in their own application — for permission to call other expert evidence, for wasted costs, for committal — the wording should cover the defence costs.

Run-off cover. For experts the run-off question matters as much as for any other professional. Claims arising from expert work can take years to come through. Run-off on cessation of expert work should be planned for.

AI in expert work — the live underwriting issue

Generative AI tools are now in widespread use in professional practice generally and expert work specifically. The risks are not theoretical. The English Court of King's Bench Division in Smith v Tesco Stores Ltd [2024] (and related case law in 2025) has repeatedly criticised expert reports relying on AI-generated content without disclosure. The American jurisprudence — most prominently Mata v Avianca [2023] in the Southern District of New York — illustrates the catastrophic consequence of citing hallucinated authorities.

The Civil Justice Council's interim guidance on AI in litigation (2024) makes three points relevant to experts:

The use of AI tools in preparing expert evidence should be disclosed to the court
The expert remains personally responsible for the content of the report, regardless of the tool used to produce it
Citations to authority must be verified by the expert before being included

The PI underwriting consequence is that insurers now ask, at renewal, about the firm's or individual's policy on AI use in expert work. The substantive answer they want is that AI is used (or not used) on a controlled basis with human verification of every citation, every authority and every numerical output that goes into the expert's report. The wording risk is that hallucinated content in an expert report — citations that do not exist, calculations performed by an AI tool and not verified — sits at the intersection of expert negligence and procedural impropriety, and may generate claims that are uncomfortable to defend.

How much cover do you actually need?

Expert witness PI limits track the size of the matters the expert is instructed in.

£1m — a sensible floor for an occasional expert witness whose principal income is from their underlying profession, working in lower-value county court and tribunal matters. Often delivered as an extension to the underlying professional PI.

£2m to £5m — the standard band for active expert witnesses in mid-value commercial and family work. Standalone or as a named extension.

£10m — for experts regularly instructed in High Court Chancery, Commercial Court, TCC and Family Division matters where the matter at stake routinely runs to seven or eight figures. Construction experts, valuation experts in commercial property disputes, forensic accountants in fraud and shareholder disputes, and medical experts in catastrophic injury claims commonly need this band.

£25m+ — for experts in international arbitration, large competition law cases, group litigation orders, and similar matters where the stakes routinely exceed £25m. A small population of experts in this band, almost always within larger firms with proportionate PI arrangements.

The shape of the limit matters. Single joint expert work generates multi-party exposure on the same instruction, and the aggregate cap should be sized to absorb correlated claims from multiple instructing parties on a single matter.

Conflicts and confidentiality — practical points

The expert's overriding duty to the court does not relieve the expert of the contractual duties of confidentiality and conflict-management owed to the instructing party. The two regimes operate in parallel.

Practical points:

Maintain a documented conflict-check process at instruction and re-check on significant developments
Maintain documented information barriers where multiple experts in the same firm work on related matters
Keep contemporaneous notes on the materials considered and the materials excluded, with reasons
Document the engagement letter with the instructing party including the scope, the assumptions and the cap on liability
Document the expert's compliance with the duty to the court — declarations under PD35, CPR 35.12 joint statement participation
Maintain records for the limitation period plus a margin — six years from the act or omission for contract claims, longer for fraud or concealed claims

Special situations

The expert who is also a partner in a firm

Where the expert is a partner in a professional firm and the expert work is undertaken in the name of the firm, the firm's PI typically responds and the firm bears the loss. The expert's personal exposure is limited. Where the expert undertakes expert work in a personal capacity, the firm's PI may or may not respond depending on the wording — read carefully.

The full-time expert witness company

Companies built around expert witness work — common in medical, accident reconstruction, and forensic accounting — hold standalone PI sized for the full exposure. The wording should expressly cover all the experts in the company and their respective specialisms.

The expert retiring from active practice

Run-off on cessation of expert work is essential. Claims from expert engagements can take years to come through, particularly where the underlying litigation runs for several years before settling and the dissatisfied party then turns on the expert. Run-off of at least six years is the standard.

The expert giving evidence outside England and Wales

Experts instructed in Scottish proceedings sit under different procedural rules — the Court of Session and sheriff court rules — but the substantive position post-Kaney is broadly the same in Scotland (NJDB v JEG [2012] CSIH 51 confirms the position). Experts instructed in Northern Ireland sit under analogous CPR-derived rules. International arbitration sits under the rules of the relevant tribunal. The PI wording should cover the jurisdictions the expert works in.

How Apex helps

Apex Insurance Brokers Limited is a Bristol-based, FCA-authorised commercial insurance broker (firm reference number 724952). We arrange PI for individual experts, expert-witness practice companies, and firms whose partners undertake expert work alongside their core professional practice.

We act for you under FCA Conduct of Business rules. For experts the renewal conversation focuses on the wording specifics — the express expert witness extension, the forums covered, the SJE position, the wasted costs cover, the AI use policy, and the run-off arrangements. We do not write our own policies and we do not have a tied insurer relationship.

The terms on which we act are set out in our Terms of Business. The route to raising any concerns is on our Complaints page.

What to do next

If you are within ninety days of renewal, this is the moment to review the expert witness scope in your PI wording, the SJE position, the wasted costs cover and the AI use policy. If you are commencing expert work for the first time, or expanding from occasional to active expert practice, this is the moment to look at whether the underlying professional PI captures the activity adequately or whether a standalone arrangement is now appropriate.

To talk through your PI position with an Apex broker, see our contact page. The first conversation costs nothing and does not commit you to anything.

Frequently asked questions

Can expert witnesses be sued by the party who instructed them?

Yes. The Supreme Court in Jones v Kaney [2011] UKSC 13 abolished the long-standing immunity from suit that experts had enjoyed in respect of their conduct as experts. An expert who provides a negligent report or negligent evidence to the instructing party can be sued for the consequences. The expert remains protected against claims by the adverse party and by absolute privilege from defamation claims arising from evidence given in court.

Does my underlying professional PI cover my expert witness work?

Some wordings do, some do not, and some are ambiguous. The safest position is an express expert witness extension on the wording. Read the policy or speak to your broker before taking on substantial expert instructions.

What PI limit do active expert witnesses typically carry?

£1m for occasional work in lower-value matters, £2m to £5m for active expert work in mid-value commercial and family proceedings, £10m for High Court work at seven and eight figures, £25m and above for international arbitration and large group litigation work. Single joint expert work in particular requires a sensibly sized aggregate.

What is the position on AI use in expert reports?

The Civil Justice Council's interim guidance (2024) requires disclosure of AI use, holds the expert personally responsible for content regardless of the tool used, and requires the expert to verify citations and authorities. Hallucinated authorities in an expert report sit at the intersection of expert negligence and procedural impropriety. PI insurers ask at renewal about AI policy; the underlying claim risk is real and growing.

Does PI cover wasted costs orders against the expert?

Section 51(6) of the Senior Courts Act 1981 permits a wasted costs order direct against the expert in cases of improper, unreasonable or negligent conduct. Cover varies by wording — some carry it as a sub-limit, some exclude it. Active experts should know their position.

Does PI respond to defamation claims by an adverse party?

Evidence given in court is protected by absolute privilege. Extra-judicial repetition — in correspondence with non-parties, in published articles, in CVs — is not. Some PI wordings carry defamation as a named extension; worth having for active experts and expert authors.

How does single joint expert work affect PI?

The SJE owes the duty to all instructing parties. PI exposure on a single matter is therefore multi-party. The aggregate cap should be sized for correlated claims from multiple instructing parties on a single matter, and the wording should not carve out SJE work.

How long should I run-off PI after I stop doing expert work?

Six years from cessation is the standard, mirroring the Limitation Act 1980 primary period. Claims from expert engagements can take years to come through, particularly where the underlying litigation runs for several years before settling and the dissatisfied party then turns on the expert.

Are conflicts of interest covered?

Civil-liability cover responds to negligence claims arising from undisclosed conflicts. Deliberate non-disclosure of a known conflict typically sits outside cover. The defence rests on the documented conflict-clearance process at instruction.

I work as an expert in family courts. Is the position different?

Substantively no — the duty to the court runs the same way under the Family Procedure Rules Part 25, and the post-Kaney liability position is the same. The procedural framework differs and the exposure tends to cluster around different fact patterns — care proceedings, financial remedies, children matters. The wording should expressly cover family court work and any associated tribunal work (CAFCASS-instructed work, expert work in adoption proceedings).

Related guides

About Apex Insurance Brokers — Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority, FCA firm reference 724952. Registered in England and Wales, Companies House 07014570. Last reviewed: June 2026.

This guide is general information about Professional Indemnity Insurance for UK expert witnesses and is not advice tailored to any individual practice's circumstances. Procedural framework as set out in the Civil Procedure Rules Part 35 and Practice Direction 35 current at the date of writing. For advice on your own renewal please speak to a broker — see our contact page.

Expert Witnesses Professional Indemnity Insurance — UK Guide 2026