Brennan v R.

A jury remains the ultimate decision-maker, but it may not reject uncontradicted and substantively unchallenged expert evidence on a matter requiring psychiatric expertise without a rational and proper evidential basis. Under the structured defence in section 2 of the Homicide Act 1957, as amended, a suitably qualified psychiatrist may properly address each statutory stage, including substantial impairment and the ultimate issue.

A murder charge should not be left to the jury where the evidence as a whole could not rationally rebut diminished responsibility. Planning, apparently rational conduct, or post-offence behaviour will not suffice where the expert has addressed them and they do not undermine the psychiatric opinion.

The appellant killed Paul Simons and was tried at Chelmsford Crown Court for murder. He admitted the killing but relied solely on diminished responsibility. He had a documented history of mental-health difficulties, and the defence psychiatrist gave unequivocal evidence that recognised disorders substantially impaired his ability to form rational judgment and exercise self-control, and significantly contributed to the killing.

The Crown called no psychiatric evidence. Its case relied on the planning of the killing, the appellant's conduct before and after it, and aspects of his apparently rational behaviour. The jury convicted him of murder by a majority. He appealed against conviction, contending that the verdict was unsafe and that the murder charge should have been withdrawn from the jury.

1. Appeal allowed. The murder conviction was unsafe. It was quashed and a verdict of manslaughter substituted.

2. Although juries decide criminal cases, their verdicts must rest on evidence. A jury is not entitled to reject uncontradicted and substantively unchallenged expert evidence on a matter within psychiatric expertise merely because the ultimate verdict is formally its responsibility. There must be a rational and proper evidential basis for rejecting the opinion.

3. Section 2 of the Homicide Act 1957, as amended by section 52 of the Coroners and Justice Act 2009, creates a more structured defence than the former provision. Its stages are predominantly psychiatric matters. A qualified expert may therefore give evidence on abnormality of mental functioning, recognised medical condition, substantial impairment, causal explanation, and the ultimate issue. The court followed the approach in Matheson (1958) 42 CAR 145, Bailey (1978) 66 CAR 31 and Pearce [2000] WL 281235.

4. A trial judge has power to withdraw murder from the jury at the close of the evidence. The question is whether, considering the expert evidence and any other evidence together, a properly directed jury could properly convict of murder. The other evidence must be capable of rebutting diminished responsibility; the exercise is likely to be unusual, but is not subject to a separate legal test of exceptionality.

5. Here, the planning, deception, and post-killing conduct had all been put to Dr Mezey. She gave an unchallenged psychiatric explanation for their consistency with diminished responsibility. The Crown called no expert evidence to undermine it. The summing-up also invited the jury to rely on the appellant's apparently coherent life in an area on which the unchallenged psychiatric evidence had directly explained the limits of lay inference. No rational basis existed for rejecting the defence. Further grounds concerning the summing-up, adverse inference direction, and sentence did not require determination. Sentencing was adjourned for further psychiatric and prison reports.

• Court of Appeal (Criminal Division): Allowed the appeal, quashed the murder conviction and substituted manslaughter. Sentencing was adjourned for further reports.
• Crown Court at Chelmsford: The appellant was convicted of murder by a majority verdict on 3 December 2013 after the jury rejected diminished responsibility.