Author and Publication
Author: Nellie Supports Ltd
Publication Date: 15/05/2026
Citation
Masterman-Lister v Brutton & Co [2002] EWCA Civ 1889.
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Abstract
This guide sets out what solicitors need from a CPR Part 35 compliant mental capacity expert: what to include in a letter of instruction, how independence and the expert's overriding duty to the court are maintained, what a compliant report should contain, realistic timescales, and how Part 35 questions are handled after delivery.
CPR Part 35: A Solicitor's Guide to Instructing a Mental Capacity Expert
This guide is written for solicitors instructing a mental capacity expert where the report will be relied on as expert evidence in civil proceedings. It explains what CPR Part 35 requires of the expert, what a strong letter of instruction contains, and how a compliant report should be structured so the evidence survives scrutiny. Nellie Supports prepares CPR Part 35 compliant capacity reports through a permanent employed team, with every report peer reviewed before delivery.
What CPR Part 35 requires of a capacity expert
CPR Part 35 governs expert evidence in civil proceedings in England and Wales. The expert's overriding duty is to the court, not to the instructing party. In a capacity report, that duty shapes everything: the expert must set out their instructions, the material relied on, the range of opinion where it exists, and the reasoning that connects the evidence to the conclusion. A report that states a conclusion without showing the reasoning is the single most common target for challenge.
What to include in the letter of instruction
A clear letter of instruction identifies the specific decision in question, the proceedings, the issues the expert must address and the documents provided. Because capacity is decision-specific under the Mental Capacity Act 2005, an instruction that asks whether a person has capacity in general terms invites a report that answers the wrong question. Name the decision, the relevant timeframe and any known impairment or diagnosis, and enclose the records that bear on them.
Independence and the expert's overriding duty to the court
An expert's primary duty is to the court, not to the party paying for the report. In practice that means the expert should be willing to reach a conclusion unhelpful to the instructing party, should identify the limits of their expertise, and should distinguish fact, observation and opinion throughout. Nellie Supports assessors work within a permanent multidisciplinary team, and every report passes internal peer review, which exists precisely to test independence and reasoning before the court ever sees the document.
What a CPR Part 35 compliant capacity report should contain
A compliant report should set out the instruction and the specific decision addressed, the documents and evidence reviewed, the relevant information for that decision, the practicable steps taken to support the person, the functional test applied under the Mental Capacity Act 2005, the diagnostic stage, the causative link between any impairment and the functional inability, and a clearly reasoned conclusion. It should also include the expert's declaration of independence, statement of truth and confirmation of compliance with CPR Part 35.
Timescales for litigation-ready reports
Timescales depend on urgency, the complexity of the decision and the volume of records to review. As a general guide, straightforward instructions can usually be completed within 7 to 14 working days of assessment, with urgent matters prioritised where the litigation timetable requires it. Solicitors should flag any court-imposed deadlines at the point of instruction so the assessment and report can be scheduled accordingly.
Part 35 questions and post-report clarification
Once a report is delivered, the instructing party or the other side may raise written questions under CPR Part 35.6. A compliant expert should remain available to answer reasonable clarification questions, provide further reasoning where the original report is challenged, and, where appropriate, participate in discussions between experts or provide a supplementary statement. Solicitors should check at the point of instruction whether this ongoing availability is included or separately chargeable.
Common pitfalls that weaken capacity evidence in litigation
The most common weaknesses in capacity evidence are a report that addresses capacity in general terms rather than the specific decision, a letter of instruction that does not identify the actual proceedings or issues, a missing or unclear declaration of independence, and a conclusion that is not clearly linked to the functional test. Reports that rely on diagnosis alone, without functional analysis specific to the decision, are also more likely to be challenged.
Single joint experts and jointly instructed reports
Where the parties agree to instruct a single joint expert, the letter of instruction should be agreed between all instructing solicitors before it is sent, and any subsequent contact with the expert should normally be copied to all parties. A single joint expert owes the same overriding duty to the court and should not be treated as favouring the party who first made contact or arranged payment.
Key takeaway for instructing solicitors
The strongest capacity evidence in litigation comes from a clear, decision-specific letter of instruction and an expert who explains independence, methodology and reasoning as thoroughly as the conclusion itself. Building CPR Part 35 compliance into the instruction from the outset reduces the risk of the report being challenged on procedural or evidential grounds later in proceedings.
Frequently asked questions
Does every capacity report need to comply with CPR Part 35?
No. CPR Part 35 applies where a report is being used as expert evidence in civil proceedings. A capacity assessment prepared for a family or for administrative purposes, such as an LPA registration, does not need to meet the same evidential standard unless it may later be relied on in contested proceedings.
What should a letter of instruction include?
The letter of instruction, the pleadings identifying why capacity is in issue, the medical and care records and any earlier assessments. Under Part 35 the report must state the substance of all material instructions, so instructions should be written on the assumption the court will read them.
How long does a CPR Part 35 compliant capacity report take?
A Part 35 compliant report is needed whenever capacity evidence will be relied on in civil proceedings: protected party questions, settlement approvals and contested capacity issues all require evidence that meets the rules, prepared with the court's permission in mind.
Related mental capacity assessment pages
These internal links help readers move from this guide to the most relevant Nellie Supports service page, assessment option or legal framework page.
Need to instruct a CPR Part 35 compliant capacity expert?
Nellie Supports provides independent, decision-specific capacity assessments prepared for use in civil proceedings, with over 11,000 assessments completed and internal peer review on every report. Call 0333 987 5118 or send an enquiry and our client liaison team will respond the same working day.