R v Kemp (1957) 1 QB 399
Physical impairment as a “disease of the mind” in the law on insanity
Facts
The defendant assaulted his wife with a hammer. He had no previous history of violence and no apparent motive. He was charged with causing grievous bodily harm contrary to the Offences Against the Person Act 1861. The defendant argued that the attack was the result of loss of consciousness linked to arteriosclerosis, with the hardening of the arteries causing congestion of blood in his brain. This was used by the defence as grounds for a defence of automatism. The trial judge however directed the jury that the appropriate defence was one of insanity.
Issues
The issue before the appeal court was whether the trial judge had correctly directed the jury that insanity is the appropriate defence in this case and more broadly whether the M’Naghten “disease of the mind” test can apply to physical conditions as well.
Decision/Outcome
The court held that hardening of the arteries could amount to a disease of the mind due to its effect on a person’s reasoning ability. Essentially the court was not concerned with how a defendant got to a certain state of mind (through a physical or psychological impairment), but that he reached that state and was in it at the time of committing the offence. The term “disease of the mind” was designed, inter alia, to limit the effect of the term “defect of reason” so as not to permit stupidity to act as a defence. The trial judge had therefore been correct in directing the jury that the appropriate defence is insanity and not automatism.
Updated 20 March 2026
This article accurately summarises the facts, issues, and decision in R v Kemp [1957] 1 QB 399. The case remains good law and continues to be cited as authority for the proposition that a physical condition can constitute a “disease of the mind” for the purposes of the M’Naghten rules, provided it affects the defendant’s mental faculties.
Readers should note, however, that the law on insanity and automatism in England and Wales has been the subject of sustained criticism and law reform proposals. The Law Commission published a report, Criminal Liability: Insanity and Automatism (2013), recommending that the M’Naghten rules be replaced with a modern statutory framework. As of the date of this note, no legislation implementing those recommendations has been enacted, so the M’Naghten rules — and Kemp as an application of them — remain operative. The broader distinction between insane and non-insane automatism, and the sometimes counterintuitive results it produces in cases involving physical conditions, continues to be a live area of academic and reform debate.
