What to Expect from a Psychiatric Expert Witness Assessment

Psychiatry vs Psychology: Understanding the Distinction

Solicitors sometimes use "psychological" and "psychiatric" interchangeably, but the two disciplines are distinct. A psychiatrist is a medically qualified doctor who has completed specialist training in mental disorders. Psychiatrists can diagnose mental illness under ICD-11 or DSM-5, prescribe medication, and provide opinions on treatability and prognosis. A psychologist is not a medical doctor and focuses on cognitive functioning, behaviour, and psychological testing.

For referral questions involving a formal psychiatric diagnosis — schizophrenia, bipolar disorder, severe depression, personality disorder — a psychiatrist is the appropriate expert. For questions about cognitive ability, learning disability, PTSD symptom severity, or suggestibility, a psychologist is typically instructed. In complex cases, both experts may be required.

Forensic psychiatrists hold specialist training in the interface between mental disorder and the law. They are the appropriate experts for fitness to plead assessments, diminished responsibility opinions, and Mental Health Act recommendations in criminal proceedings.

Stage One: Instruction and Document Review

The instruction process follows the same framework as any expert witness instruction. Your letter of instruction should set out the background facts, the specific questions the psychiatrist is asked to address, and the documents provided. Psychiatric assessments typically require a broader set of records than psychological assessments — GP records, hospital discharge summaries, community mental health team (CMHT) notes, and any previous psychiatric reports are all relevant.

Where your client has a history of contact with mental health services, obtaining those records before instruction saves time. The psychiatrist will request them if not provided, which adds to the overall timeline. In legally aided cases, prior authority should be in place before the assessment appointment is booked.

Stage Two: The Psychiatric Assessment Appointment

A psychiatric assessment appointment typically lasts between one and three hours. Unlike a psychological assessment, it does not involve standardised psychometric testing as the primary tool — instead, the psychiatrist conducts a structured clinical interview and a mental state examination (MSE). The MSE is the core diagnostic instrument in forensic psychiatry.

The Mental State Examination

The MSE assesses the following domains at the time of the interview:

The MSE captures the client's presentation at the time of interview. It does not necessarily reflect their mental state at the time of the alleged offence. Where the referral question concerns historical mental state — for example, diminished responsibility — the psychiatrist reconstructs the historical picture from records, witness accounts, and the client's own account.

Psychiatric History

The psychiatrist takes a full psychiatric history covering: presenting complaint, history of the current illness, past psychiatric history, past medical history, family history of mental illness, personal history (developmental, educational, occupational, relationship), forensic history, substance use history, and premorbid personality.

This history is cross-referenced against the records provided. Where the client's account conflicts with the clinical records, the psychiatrist will note the discrepancy and explain how it affects their opinion.

Stage Three: Diagnosis and Formulation

Following the interview and records review, the psychiatrist formulates a diagnosis using ICD-11 (or DSM-5 where specified). The report will set out the diagnostic criteria met, the evidence supporting the diagnosis, and any differential diagnoses considered and excluded.

The clinical formulation goes beyond diagnosis. It explains how the individual's history, mental disorder, and circumstances interact to produce the behaviour under examination. In a diminished responsibility case, for example, the formulation links the diagnosis to the abnormality of mental functioning and explains how that abnormality substantially impaired the defendant's ability to form a rational judgement or exercise self-control.

Stage Four: The Psychiatric Report

The psychiatric report follows the same structural requirements as any expert report under CrimPR Rule 19, CPR Part 35, or FPR Part 25. It must include a statement of truth, a declaration of overriding duty to the court, and a clear separation of fact and opinion.

A well-structured psychiatric report contains:

1. Instructions received, documents reviewed, and qualifications of the expert
2. Psychiatric history (derived from interview and records)
3. Mental state examination findings at the time of assessment
4. Diagnosis with ICD-11 criteria and differential diagnoses
5. Clinical formulation linking diagnosis to the referral questions
6. Opinions addressing each question in the letter of instruction
7. Recommendations (where relevant — e.g., treatment, disposal options)
8. Statement of truth and compliance declaration

Standard turnaround from the assessment appointment is ten to fifteen working days. Complex cases — for example, those requiring review of extensive hospital records or a second assessment session — may take longer. Urgent turnaround can be requested at the point of instruction.

Stage Five: Court Attendance

Psychiatric experts are frequently required to give oral evidence, particularly in Crown Court trials where the defendant's mental state is in issue. The psychiatrist will give evidence in chief — confirming their report and expanding on key findings — before being cross-examined by opposing counsel.

Forensic psychiatrists are experienced in court. They understand that their duty is to the court, not to the instructing party, and they will maintain their opinion under cross-examination where the clinical evidence supports it. Where the cross-examination raises a genuinely new clinical point, the expert may acknowledge it and, if necessary, qualify their opinion.

Court attendance fees are charged at the expert's agreed daily or half-day rate. Confirm these at the point of instruction to avoid disputes. Expert Witness UK provides a written fee schedule with every instruction confirmation.

Frequently Asked Questions