The expert witness practice of psychiatrists is under constant scrutiny by the courts and, in the UK, the General Medical Council, as well as within appraisal and revalidation as part of a doctor's overall practice. Regulation and appraisal of expert witness practice must address not only technical competence, including demonstration of a real understanding of the interface between medicine and law, but also ethical probity, including in respect of bias, which is the most challenging appraisal focus. In psychiatry, there is much room for ‘values expression’, and therefore bias, in the offering of expert opinion. This article first describes various legal and psychological definitions of bias; then addresses the sources and routes to expression of bias within expert witness practice, viewed legally, psychologically and neuroscientifically. Finally, it proposes ways in which inevitable bias can be minimised by the individual practitioner.

The new Sentencing Council Guideline on sentencing offenders with mental disorders, effective from 1 October 2020, is essential reading for all psychiatrists who give evidence in the criminal courts, revealing something of required judicial thinking, our common ground on public safety concerns but differences in focus on culpability and punishment.

Acting as an expert psychiatric witness can be rewarding, but there are potential costs and pitfalls, such that the role should be undertaken only in an informed manner. With reference to the recent disciplinary cases of Dr Richard Pool and Dr Waney Squier, and a judgment of the Supreme Court, advice is offered to potential expert psychiatric witnesses. Suggestions are made as to training, the negotiation of instructions, the citation of published literature, the construction of expert opinion and how to ensure compliance with the ethical duties of the expert witness.

The professional regulatory cases of the psychiatrist Dr Richard Pool and the neuropathologist Dr Waney Squier have given rise to concerns among expert psychiatric witnesses, and indeed medical experts in general. Here we restate the law on expert evidence with particular reference to the judgment of the Supreme Court in the case of Kennedy v Cordia. We emphasise that Pool does not change the law regarding ‘what is expertise’; in particular, the case does not establish restrictive, status-based tests governing the admissibility of expert evidence such as according to whether an expert psychiatric witness has undergone higher training, is on the specialist register as a specialist in a particular field or is a consultant. Rather, expertise continues to be legally defined in terms of a combination of qualification, knowledge and experience. Crucially, the test of medical expertise in legal proceedings is a legal test and not one determined within a medical paradigm.

Srinivas et al provide a comprehensive guide to the law, regulations and practice concerning the management of ‘restricted patients', who are the responsibility of both the clinical services treating them and the Home Office. In doing so, they make the assumption, with apparent approval, that there is a ‘partnership’ between clinicians and the Home Office. However, partnership assumes parties working towards a common goal on an equal footing. Neither assumption is correct here. Although forensic mental health services direct themselves explicitly towards enhancing public safety, they do so in conjunction with treatment aimed at the relief of dysphoria in the patient. The interest of the Home Office in the patient's mental health is solely in terms of its impact on the risk of harm to others. There is therefore no ‘partnership’. Rather, there is constructive tension between agencies working towards differently valued and balanced objectives. Certainly the relationship is not one of equal power.

There is no direct coherence between medical and legal concepts or between medical and legal ways of thinking (Eastman, 1992). As a result, there are often substantial difficulties in translating the findings of one (medicine) into the decisions of the other (law). In order to minimise interdisciplinary confusion, it is necessary for each to have an understanding of the approach of the other. This paper attempts to elucidate the relationship between law and psychiatry as it is played out specifically in personal injury litigation and in relation to civil legal claims for (legal) ‘nervous shock’. It is not confined solely to claims arising out of the development of post-traumatic stress disorder (PTSD) (Eastman, 1995; Napier, 1995), but is applicable to any psychiatric sequelae of events for which legal liability of a defendant can be established. It also offers general comments about the provision of civil psycho-legal assessments, advice and opinion writing (Carson et al, 1993) as a backcloth to its more specific purpose.