R v Johnson  EWCA Crim 1978
Inapplicability of insanity defence where defendant is aware of illegality of actions
J was convicted of wounding with intent to cause grievous bodily harm. Following his arrest, he was diagnosed with paranoid schizophrenia and it was agreed that he had been suffering from this at the time of the attack. At trial, the plea of insanity was not available to J because evidence suggested that he knew what he was doing was against the law.
On appeal, J submitted that he should have been found not guilty by reason of insanity on because whilst he knew what he was doing was against the law, his mental condition at the time of the attack meant that he felt that there was a moral justification for his actions. In R v Windle  2 QB 82, it was held that the defence of insanity was not available where the accused knew that what he was doing was contrary to law even where he believes his actions to be morally justified. In this case, the Court was required to consider whether a wider interpretation should be given to the defence. It had been argued that Windle set an unduly restrictive test on which to consider the responsibility of the mentally disordered.
J’s appeal against conviction was dismissed. The case of Windle clearly established that the defence of insanity in light of the M’Naghten rules applied where a defendant did not know what he was doing was legally wrong. Whilst highly persuasive arguments had been made for extending the scope of the defence in the Australian High Court case of Stapleton v R. 86 C.L.R. 358, the position of English law was to strictly follow Windle.