What Is an Expert Witness Report?
An expert witness report is a written document in which a suitably qualified expert sets out their opinion on a matter that is beyond the knowledge of the court. The report is the primary vehicle through which expert evidence is placed before the judge or jury. It is not a letter, a summary, or a clinical note — it is a formal legal document that must comply with the procedural rules governing expert evidence in the relevant jurisdiction.
In criminal proceedings in England and Wales, the governing rule is CrimPR Rule 19.4 of the Criminal Procedure Rules 2020 (SI 2020/759). In civil proceedings, the equivalent rule is CPR Part 35.10. In family proceedings, the framework is FPR Part 25, supplemented by Practice Direction 25B. Each framework imposes mandatory content requirements, and a report that fails to meet those requirements is vulnerable to challenge, exclusion, or — in the most serious cases — adverse costs orders against the instructing party.
The overriding duty that runs through all three frameworks is the expert's duty to the court. Under CrimPR Rule 19.2(1), CPR 35.3, and FPR 25.3, the expert's duty to give objective, unbiased evidence overrides any obligation to the party that instructs or pays them. A report that reads as advocacy for the instructing party — rather than an independent professional opinion — will be treated with scepticism by the court and may be excluded entirely.
The 9 Mandatory Elements Under CrimPR Rule 19.4
CrimPR Rule 19.4 sets out nine elements that every expert witness report in criminal proceedings must contain. Each element serves a distinct purpose, and the absence of any one of them is a ground for the opposing party to challenge the admissibility of the report.
Qualifications and experience
The expert's academic qualifications, professional registrations, clinical or technical experience relevant to the opinion, and any specialist accreditation. The court uses this to assess whether the expert is qualified to give the opinion.
Statement of instructions
A statement of the substance of all instructions received — including the questions the expert was asked to address. This is one of the most frequently omitted elements and a common ground for challenge.
Facts and assumptions
The facts and assumptions on which the opinion is based. Where the expert has relied on documents, assessments, interviews, or test results, each must be identified. Opinions unsupported by stated facts are vulnerable to cross-examination.
Expert's opinion
The substantive opinion on each question addressed. The opinion must be within the expert's stated area of expertise. Opinions that stray outside that area — even if well-reasoned — will be challenged and may be excluded.
Range of opinion
Where a range of opinion exists on the issue, the expert must summarise that range and explain why they hold the view they do. Failure to acknowledge a range — particularly in contested clinical matters — undermines the report's credibility.
Summary of conclusions
A clear, concise summary of the expert's conclusions. This section is what the court and opposing counsel read first. It must accurately reflect the body of the report and avoid introducing new material.
Overriding duty statement
A statement that the expert understands their overriding duty to the court under Rule 19.2 and has complied with it. This is a substantive compliance requirement, not a formality.
Signature and date
The report must be signed and dated by the expert. An unsigned report cannot be served and will be rejected by the court. Where the report is produced electronically, a typed signature with a date is acceptable.
Written declaration
A written declaration that the expert is aware of the requirements of Part 19 and that the report has been prepared in accordance with those requirements. Without this declaration, the report is non-compliant on its face.
CrimPR Rule 19.4, CPR Part 35, and FPR Part 25: How They Compare
The three procedural frameworks share the same overriding principle — the expert's duty to the court — but differ in their specific requirements for report content, the mechanism for obtaining permission to adduce expert evidence, and the procedure for joint statements. The table below sets out the key differences.
| Aspect | Criminal (CrimPR) | Civil (CPR) | Family (FPR) |
|---|---|---|---|
| Governing rule | CrimPR Rule 19.4 | CPR Part 35.10 | FPR Part 25 / PD 25B |
| Overriding duty to court | Rule 19.2 | CPR 35.3 | FPR 25.3 |
| Statement of instructions | Substance of all instructions | Written instructions in report | Substance of all instructions |
| Range of opinion | Required | Required | Required |
| Written declaration | Rule 19.4(i) | CPR 35.10(2) | PD 25B para 9.1 |
| Joint statement | Rule 19.6 | CPR 35.12 | FPR 25.16 |
| Permission to adduce | Case management directions | Court permission required | Court permission required |
The Letter of Instruction and Its Role in the Report
The letter of instruction is the document the solicitor sends to the expert setting out the background facts, the questions to be addressed, and the documents to be considered. Under CrimPR Rule 19.4(b), the expert must include in their report a statement of the substance of all instructions received. This means the report must reflect — at least in summary — what the expert was asked to do.
A well-drafted letter of instruction has a direct bearing on the quality of the report. Where the questions are vague or the factual background is incomplete, the expert is forced to make assumptions — and those assumptions must then be stated in the report under Rule 19.4(c). Assumptions that are later shown to be incorrect will undermine the opinion built on them.
The letter of instruction should include: the full name and date of birth of the subject; a summary of the alleged offence and the relevant procedural stage; the specific questions the expert is asked to address; a list of all documents enclosed; the deadline for the report; the LAA reference number and approved fee (if applicable); and confirmation of whether prior authority has been obtained.
Related guide
For a full guide to LAA prior authority applications and approved fee rates by discipline, see the Prior Authority & LAA Funding Guide.
Common Report Deficiencies and How to Address Them
The following deficiencies appear repeatedly in expert witness reports challenged in criminal proceedings. Each one is avoidable — and each one is the solicitor's responsibility to identify before the report is served.
Missing written declaration
Impact: Report is non-compliant on its face; court may refuse to admit it.
Fix: Add a dedicated declaration paragraph citing Rule 19.4(i) before the signature block.
No statement of instructions
Impact: Opposing counsel can challenge the scope of the opinion and the questions addressed.
Fix: Include a verbatim or summarised version of the letter of instruction questions in a dedicated section.
Opinion outside area of expertise
Impact: The court will exclude the opinion on that point; the expert's credibility on all other points is damaged.
Fix: The expert must explicitly state the limits of their expertise and decline to opine on matters outside it.
No range of opinion
Impact: In contested clinical matters, the court will question whether the expert has considered alternative views.
Fix: Add a paragraph acknowledging the range of professional opinion and explaining why the expert holds their particular view.
Facts and opinion not separated
Impact: The court cannot assess whether the opinion is properly grounded in the facts of the case.
Fix: Use separate sections — 'Background and Facts' and 'Opinion' — to make the distinction structurally clear.
Unsigned or undated report
Impact: The report cannot be served and will be rejected by the court office.
Fix: Ensure the expert signs and dates the final version before service. Electronic signatures with a date are acceptable.
Joint Expert Statements Under CrimPR Rule 19.6
Where both prosecution and defence have served expert evidence on the same issue, the court may direct the experts to meet and produce a joint statement under CrimPR Rule 19.6. The joint statement must identify: the matters on which the experts agree; the matters on which they disagree; and the reasons for any disagreement. It supplements the individual reports — it does not replace them.
The joint statement process serves a case management function. By identifying the real areas of dispute before trial, it allows the court to focus the oral expert evidence on the points that genuinely require judicial determination. Where experts agree on the central issue, the court may dispense with oral evidence from one or both of them entirely.
The equivalent provisions in civil proceedings are CPR 35.12 (joint statements) and CPR 35.7 (single joint experts). In family proceedings, FPR 25.16 governs the joint statement procedure. In family proceedings, the court also has power under FPR 25.11 to direct that a single joint expert be instructed rather than separate experts for each party — a direction that is more common in family proceedings than in criminal ones.
Solicitors should note that the content of a joint statement cannot be used in evidence at trial without the court's permission, except as evidence of what the experts agreed and disagreed about. The joint statement is not a substitute for the individual expert reports, and the experts remain available for cross-examination on their individual reports at trial.
Solicitor's Pre-Service Checklist
Before serving an expert witness report on the court and opposing parties, the instructing solicitor should verify each of the following points. A report that fails any one of these checks should be returned to the expert for amendment before service.