Insanity in English law

In the first situation, the defendant must show that he was either suffering from a disease which damaged the functioning of the mind and led to a defect of reason that prevented him from understanding what he was doing, or that he could not tell that what he was doing was wrong.

During the 18th century the test to determine insanity became extremely narrow, with defendants required to prove that they could not distinguish between good and evil and that they suffered from a mental disease which made them incapable of understanding the consequences of their actions.

The idea of insanity in English law dates from 1324, when the Statute de Praerogativa Regis allowed the King to take the lands of "idiots and lunatics."

[4] In many cases, the insane defendant was released and allowed to go home; in some, he was held in prison until the King decided to grant him a pardon.

[5] It was then established that somebody found not guilty due to insanity should be immediately released; up until the beginning of the 19th century, this was almost all that could be done, although the Vagrancy Act 1744 allowed two Justices of the Peace to confine a dangerous lunatic.

Several medical experts testified that Hadfield's injuries at the Battle of Tourcoing, where he was repeatedly struck in the head by a sabre, had caused insanity,[8] and Lord Kenyon immediately sent the jury away to reach a decision.

[11] On 20 January 1843, Daniel M'Naghten attempted to assassinate Robert Peel, Prime Minister of the United Kingdom.

[12] He was assisted in his defence by two solicitors, four barristers including Alexander Cockburn and nine medical experts, along with eight lay witnesses.

In R v Quick and Paddison [1973] QB 910, for example, the courts decided that an assault committed when the defendant was suffering from hypoglycemia due to the taking of insulin was not insane in nature, while in R v Hennsey [1989] 1 WLR 287 it was held that a crime committed while the defendant was suffering from hyperglycemia did constitute insanity.

As a result, the existing law allows some diabetics to be acquitted while others are declared insane, something one academic describes as "absurd".

[25] In R v Sullivan, a man was charged with grievous bodily harm under the Offences against the Person Act 1861 after assaulting his friend during an epileptic seizure.

[28] The Butler Committee proposed reform, which was repeatedly ignored by successive governments; the Law Commission drafted a Criminal Code Bill in 1989 which altered the rules on insanity, but this was again ignored.