R v Kemp [1957] 1 QB 399 holds that a physical disease affecting the mental faculties can amount to a “disease of the mind” under the M’Naghten Rules.
Facts of the Case
The accused, Albert Kemp, an elderly man of excellent character devoted to his wife, made an entirely motiveless and irrational attack on her, causing a grievous wound. Medical evidence showed he suffered from arteriosclerosis, causing a congestion of blood in the brain that produced a temporary lapse of consciousness during which the attack occurred. All experts agreed he was not conscious of his actions and was therefore not responsible for them.
The Judgment
The issue was whether arteriosclerosis was a “disease of the mind”. Devlin J held that it was. The law is concerned with the “mind” — the faculties of reason, memory and understanding — rather than the physical organ of the “brain”. He clarified that:
- Origin is irrelevant: the law does not distinguish diseases of mental from physical origin; only the resulting mental state matters.
- Duration is irrelevant: the condition may be permanent or transient — “temporary insanity” suffices.
- Limitation of the rules: “disease of the mind” limits the “defect of reason” defence so it does not apply to acts caused by mere “brutish stupidity” or an untrained mind.
Wider Context of the Time
The case was decided under the Trial of Lunatics Act 1883, which introduced the special verdict of “guilty but insane” — a “qualified acquittal” keeping violent insane defendants in custody “until Her Majesty’s pleasure be known”, replacing the earlier absolute acquittal.
Related Cases
- M’Naghten’s Case (1843): established the insanity defence — a “defect of reason, from disease of the mind”.
- Regina v Charlson (1955): distinguished; there the doctors agreed there was no disease of the mind, giving an absolute acquittal, whereas in Kemp they disagreed, requiring a legal definition.
- Criminal Lunatics Act 1800: an earlier statute on insanity and unfitness to plead.