R v Kemp (1957) 1 QB 399

Physical impairment as a “disease of the mind” in the law on insanity


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.


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.


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.