A senior partner at a chartered quantity surveying practice in the South West is instructed as expert witness for the defendant employer in a £4.8m adjudication brought by a main contractor over a disputed final account on a healthcare scheme. The expert's report concludes that the contractor's loss-and-expense quantification is overstated by roughly £2.1m, that the variation pricing applies the wrong tender rates to several substantial change items, and that the contractor's programme delay analysis fails to satisfy the SCL Delay and Disruption Protocol methodology. The adjudicator finds substantially for the defendant employer; the contractor pays close to nothing of the pleaded sum. Eight months later the contractor's solicitors write to the expert's firm alleging negligent expert evidence — specifically, that the delay-analysis methodology selected was not appropriate to the contract form, that key documents disclosed in adjudication were not properly addressed, and that the report's conclusions were therefore unreliable. The pleaded loss is the contractor's costs of pursuing the failed adjudication, the sums the contractor says it would have recovered on a competently-presented case, and the contractor's onward costs of the resulting commercial dispute — totalling some £1.9m.
That letter, addressed not to the practice's underlying engagement but to its expert witness work, is the claim pattern this article is about. Expert witness exposure has changed materially since the Supreme Court's decision in Jones v Kaney in 2011 removed the witness immunity that had previously protected experts from being sued by the party that instructed them. This article looks at the QS as expert witness in adjudication, arbitration, TCC and dispute board proceedings; the duties owed to the court under CPR Part 35; the methodology-error claim pattern that is the dominant expert-witness PI exposure; what insurers exclude and what they cover; and how the activity should be flagged on the PI proposal form. It sits within the quantity surveyors PI pillar guide and is the sibling article to our cost overrun disputes cluster.
The QS as construction expert
A chartered quantity surveyor is one of the most frequently instructed expert witnesses in UK construction disputes. Quantum, delay, loss-and-expense, variation valuation, final-account analysis, defects costing, prolongation cost analysis, disruption analysis, repudiation valuation, mitigation assessment — most of the technical expert work in construction disputes sits within the QS's territory or overlaps closely with it. The role attracts senior practitioners — partners and directors with substantial project experience, often with formal expert-witness training (Academy of Experts, Expert Witness Institute, RICS Expert Witness accreditation), and a settled track record of writing reports that withstand cross-examination.
The forums in which the expert work is conducted shape the procedural framework. Adjudication under the Housing Grants, Construction and Regeneration Act 1996 (as amended) is the dominant first-instance forum for construction disputes — a 28-day statutory process (extendable by agreement), with the adjudicator's decision binding on an interim basis. Expert reports in adjudication are typically shorter, more focused, and produced to extremely tight deadlines. Arbitration under bespoke agreement or the rules of bodies such as the LCIA or ICC handles the larger commercial disputes where the parties want a binding final award. The Technology and Construction Court (TCC) within the High Court is the specialist court for construction litigation, with its own pre-action protocol and procedural rules. Dispute boards (DRB, DAB, DAAB) — increasingly common on large infrastructure schemes under FIDIC and NEC4 — handle disputes on an in-project, rolling basis.
Each forum has its own deadline pressure, its own evidential standards, and its own expectations about the conduct of expert evidence. What is constant across all of them is the expert's duty: the expert's overriding duty is to the tribunal, not to the instructing party.
CPR Part 35 — the duty to the court
Civil Procedure Rules Part 35 governs expert evidence in TCC proceedings (and in arbitration and adjudication by analogy and by the rules of the relevant tribunal). The framework is straightforward in principle and demanding in practice.
CPR 35.3 establishes 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." This is the foundational principle: the expert is not the instructing party's advocate. The expert's report is for the tribunal's benefit, not for the party's case-building. An expert who tailors evidence to the instructing party's preferred outcome — who omits adverse considerations, who advances theories the expert does not actually hold, who declines to address the documents — has breached the Part 35 duty and risks both the report being given little weight and personal professional consequences.
The Part 35 Practice Direction and the associated Guidance for the Instruction of Experts in Civil Claims (most recently revised in 2014, with further guidance from the Civil Justice Council) set out the form and content requirements for expert reports: independence statement, statement of truth, statement of compliance with the expert's duty, summary of conclusions, reasoning, methodology, sources, limits and qualifications. Departures from the form requirements weaken the report's evidential weight; departures from the substantive duty expose the expert to professional discipline and, since 2011, to civil claim.
Jones v Kaney — the end of expert immunity
For centuries the common law afforded expert witnesses immunity from suit by the parties they served, on the rationale that experts should be free to give frank evidence without fear of being sued by a disappointed instructing party. That immunity was removed by the Supreme Court in Jones v Kaney [2011] UKSC 13 — a clinical-negligence case in which the claimant sued his own expert for allegedly conceding ground in a joint statement that materially weakened his case.
The Court held by a 5-2 majority that the historical immunity could no longer be justified. The expert remains protected, like any other witness, from defamation claims arising from evidence given in court, but is exposed to claims in negligence by the party that instructed and paid for the expert's services. The decision applies across all expert disciplines, including construction.
The practical effect for construction experts has been a substantial increase in the visibility of the activity to PI underwriters. Underwriters now treat expert witness work as a defined exposure category — disclosed on the proposal form, assessed for frequency and value, sometimes endorsed with a specific sub-limit or notification trigger, occasionally excluded from cover entirely for firms doing high volumes of contentious work. The activity is insurable on standard RICS-approved wordings, but the wording details matter.
The methodology-error claim pattern
The dominant claim pattern in expert-witness PI is the methodology error. The losing party — or in some cases the winning party, where the win was smaller than hoped — alleges that the expert's report applied the wrong methodology, applied the right methodology incorrectly, missed key documents, or reached conclusions that could not properly be sustained on the analysis presented.
Common formulations include: in delay analysis, that the expert applied (say) a time-impact analysis where windows analysis would have been appropriate, or applied a chosen methodology without proper basis; in loss-and-expense quantification, that the expert used global-claim assumptions where the underlying records permitted granular analysis, or failed to apportion concurrent causes; in variation valuation, that the expert applied tender rates to variations that should have been valued at fair rates, or vice versa; in defects costing, that the expert applied repair costs where replacement was reasonable, or failed to factor betterment.
The defence runs on the technical merits — that the methodology selected was within the range of approaches a reasonably competent expert would have adopted on the available material — and on the procedural framework — that the expert complied with CPR Part 35, that the report was independent, that the conclusions were properly reasoned, that the limits and qualifications were stated. As with cost-overrun claims against the firm's underlying QS work (covered in the cost overrun cluster), the strength of the defence usually tracks the quality of the contemporaneous file — the working papers, the document-review records, the methodology rationale, the joint-statement preparation notes.
Defence costs on a contested expert-witness PI claim broadly mirror the defence-cost profile for underlying-work claims: low five-figures on a straightforward early-settled matter, mid- to high-six-figures on a contested TCC trial. The claimant in an expert-witness claim faces a high evidential bar — they need to show not just that the expert's evidence was suboptimal but that competent expert evidence would have produced a materially different outcome — which is itself a substantial undertaking and one that limits the universe of viable claims.
What insurers exclude — and what they cover
Most RICS-approved QS PI wordings cover expert witness work as part of the firm's professional activities, but the cover is not uniform. The variables that matter are the following.
Activity declaration. The proposal form will ask explicitly whether the firm undertakes expert witness work, the proportion of fee income, the typical case value, the forums (adjudication, arbitration, TCC), and the basis (party-appointed, single joint expert, court-appointed). Honest, complete declaration is a duty under the policy and a precondition to cover; underwriters who later discover undeclared expert practice can decline cover or void the policy.
Sub-limits or specific endorsements. Some wordings apply a sub-limit to expert witness work — for example, capping cover at a defined figure per expert engagement, or aggregating across the policy year. Where the firm's expert practice is substantial relative to its overall fee income, a sub-limit can leave material exposure uninsured.
Exclusions. Some wordings exclude expert evidence on contingent fees (where any element of the expert's remuneration depends on the outcome — generally regarded as inconsistent with CPR Part 35 in any event). Some exclude defamation or honest-but-incorrect-statement claims that fall outside the post-Jones-v-Kaney negligence framework. Some exclude work undertaken in non-UK forums or under non-UK law.
Notification triggers. Some wordings include specific notification triggers for expert-witness engagements — for example, requiring the firm to notify when instructed on a matter exceeding a defined value, or when serving in a defined forum. Failure to notify on the trigger can prejudice cover for any subsequent claim arising from that matter.
Conduct during proceedings. Most wordings include conduct conditions — the expert must comply with the tribunal's directions, must observe the relevant procedural rules, must not act outside the scope of the instructions. Breach of these conditions does not automatically void cover but can give the insurer grounds for declining particular claims.
The wording variables make broker review of the proposal form and policy schedule the practical difference between insured and uninsured expert practice. Apex's standard renewal process includes specific review of the expert-witness declaration and the schedule provisions where the firm holds itself out as an expert.
How to flag expert work on the proposal form
The proposal-form declaration is the foundation of cover for expert practice. Standard practice is to declare the activity explicitly, with the following information.
Whether the firm undertakes expert witness work at all — the binary answer. The number of expert engagements in the preceding 12, 24 and 36 months. The fee income from expert work as a proportion of total fee income. The typical value of the matters on which the firm is instructed, with a range (lowest, typical, highest). The forums (adjudication, arbitration, TCC, dispute board, others). The basis of instruction (party-appointed, single joint expert, court-appointed, advisory only). Whether the firm has acted as expert in any matter that has settled adversely or been the subject of a complaint. Whether any complaint or claim has been made against the firm in respect of expert work in the preceding seven years. Whether the firm holds formal expert-witness accreditation (Academy of Experts, EWI, RICS Expert Witness Registration).
The narrative — what kind of expert work, in what sector, to what level of contention — is at least as important as the figures. A well-presented declaration that frames the practice's expert work alongside the firm's broader QS work, with examples of forums and a coherent description of the firm's internal quality controls on expert reports, tends to produce better renewal terms than a bald yes-with-figures.
Where expert practice intersects with the firm's underlying work
A claim of particular sensitivity arises where the firm's expert in one matter previously acted as the firm's QS on the underlying project — typically as employer's agent, contract administrator or cost consultant — and is now giving evidence in the dispute that has arisen from that project. Acting as expert in a dispute the firm was substantively involved in raises independence questions under CPR Part 35; in most cases another expert from outside the firm should be instructed, and the original-engagement practitioner serves as a factual witness instead.
A related issue is the firm being sued on its underlying work (as in our cost overrun cluster) at the same time as being separately retained as expert in unrelated matters. The two notifications are separate; both are insured under the same RICS-approved policy provided the wording covers both activities; the management of the two streams runs separately through the insurer's claims function.
Working with the broker on expert practice
For firms with substantial expert practice the broker conversation is annual and detailed. The wording should be specifically reviewed for expert-witness provisions; the proposal form should be completed with the activity properly framed; any matters notified in respect of expert work should be presented to the renewing market with a clear narrative; and the firm should be advised on whether the limit and aggregation are sized to the activity profile.
Apex works regularly with chartered QS practices that have an active expert-witness practice alongside the firm's underlying cost-consultancy and contract-administration work. The renewal process is built around the specifics of the firm's portfolio — the expert work is treated as a distinct exposure within the broader account, with the wording and the limit shaped accordingly.
How Apex helps
Apex Insurance Brokers is an independent FCA-authorised insurance broker. We act as the firm's broker under the Financial Conduct Authority's Conduct of Business rules, representing the firm's interests in the negotiation with the RICS-approved PI market. The terms on which we act are set out in our Terms of Business, our handling of personal data in our Privacy notice, and the route for raising concerns about our service is on our Complaints page.
The quantity surveyors sector page is the place to start a renewal conversation, or contact us directly. If you are within ninety days of renewal this is the moment to review whether your wording and limit are sized to your expert practice; if you have a complaint or claim in connection with expert work, that conversation is the priority — late notification on expert matters carries the same consequences as late notification on any other PI matter.
Frequently asked questions
Does my standard QS PI policy cover expert witness work?
Most RICS-approved QS PI wordings cover expert witness work as part of the firm's professional activities, but the activity must be declared on the proposal form and the schedule should be checked for any sub-limits, specific exclusions or notification triggers. Undeclared expert practice can be a basis for the insurer to decline cover or void the policy. Where the firm's expert work is a material share of fee income, the broker should specifically review the wording and may recommend a tailored endorsement.
What was the impact of Jones v Kaney on expert PI?
The Supreme Court in Jones v Kaney [2011] UKSC 13 removed the historical immunity that had protected expert witnesses from being sued by the parties that instructed them. Experts can now be sued in negligence by their own instructing party. The decision applies across all expert disciplines, including construction QS work. The practical consequence for PI is that expert witness work is now treated as a defined exposure category by underwriters, with explicit proposal-form declaration and sometimes specific endorsements or sub-limits.
What duties do I owe under CPR Part 35?
CPR Part 35 establishes that the expert's overriding duty is to the tribunal, not to the instructing party. The expert must give independent, objective opinion within their expertise; comply with the form and content requirements of the Practice Direction; state the substance of all material instructions; include a statement of truth and a declaration of compliance with the expert's duty. The duty applies in adjudication, arbitration and TCC proceedings (the latter directly, the former by analogy and tribunal rule). Breach of the Part 35 duty exposes the expert to professional consequences and, since 2011, to civil claim.
How is a methodology-error claim defended?
The defence runs on the technical merits — that the methodology selected was within the range a reasonably competent expert would have adopted on the available material — and on the procedural framework — that the expert complied with CPR Part 35 and equivalent rules. The contemporaneous file is the key defensive asset: the working papers, the document-review records, the methodology rationale, the joint-statement preparation notes. The claimant must show not just suboptimal evidence but that competent evidence would have produced a materially different outcome, which is a high bar.
Can I act as expert in a dispute on a project my firm worked on?
In most cases no. Acting as expert in a dispute the firm was substantively involved in raises independence questions under CPR Part 35 and equivalent rules — the expert's overriding duty to the tribunal is hard to reconcile with the firm's prior commercial interest. The conventional position is that another expert from outside the firm is instructed, and the original-engagement practitioner serves as a factual witness. The broker can advise on how the dual-role question interacts with the PI position.
What do I declare on the proposal form?
Whether the firm undertakes expert work at all; the number of engagements over the preceding 12, 24 and 36 months; the fee income from expert work as a proportion of total fee income; the typical value of matters; the forums (adjudication, arbitration, TCC, dispute board); the basis of instruction (party-appointed, single joint, court-appointed); whether any complaint or claim has been made against the firm in respect of expert work in the preceding seven years; and whether the firm holds formal expert accreditation. The narrative around the figures is as important as the figures themselves.
What happens if a complaint is made about my expert evidence?
It is a notifiable circumstance. Whether or not the complaint hardens into a letter of claim, the firm should notify insurers through the broker promptly. Notification preserves the policy's response and is not in itself an admission of liability. Where the complaint runs to formal professional-conduct proceedings (RICS, Academy of Experts, EWI), the broker can advise on whether the policy's regulatory-defence provisions extend cover to those proceedings or whether separate arrangements are appropriate.
Related guides
- Quantity surveyors PI insurance — UK guide 2026 (pillar)
- QS PI and cost overrun disputes
- Quantity surveyors sector page — speak to a broker
- All Apex PI sectors
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. Trading address QCS, 53 Queen Charlotte Street, Bristol BS1 4HQ; registered office c/o Westcan, 5 Anglo Office Park, Bristol BS15 1NT. Email info@apexinsurancebrokers.co.uk, telephone 0117 325 0027. This article is general information about Professional Indemnity Insurance for construction expert witness work and is not advice tailored to any individual firm's circumstances. Last reviewed: May 2026.
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