The insanity defence concerns the defendant’s mental state at the time of the alleged offence. Where it succeeds, the verdict is not guilty by reason of insanity – an acquittal, but one that allows the court to make a hospital order or other protective order. It is a different question from fitness to plead, which concerns the defendant’s condition at the time of trial (see pritchardcriteria.uk).
Where the rules come from
In 1843 Daniel M’Naghten shot and killed Edward Drummond, secretary to the Prime Minister, Sir Robert Peel, whom M’Naghten appears to have believed he was shooting under the influence of persecutory delusions. His acquittal on the ground of insanity caused public outcry, and the House of Lords put a series of questions to the judges. Their answers, given by Tindal CJ, became the M’Naghten Rules, which remain the test in England and Wales today.
The test
Every defendant is presumed sane. To establish insanity, it must be shown that at the time of the act the defendant was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act they were doing – or, if they did know it, that they did not know it was wrong. There are four elements.
1. Defect of reason
The defendant’s powers of reasoning must have been impaired, not merely left unused. Absent-mindedness or confusion in someone whose reasoning is intact is not enough: in R v Clarke [1972] 1 All ER 219, a woman with depression who absent-mindedly took items from a shop had a defect of concentration, not a defect of reason.
2. Disease of the mind
This is a legal concept, not a psychiatric one, and it is far wider than mental illness. The courts have treated any internal cause that impairs the functioning of the mind as a disease of the mind, whether its origin is mental or physical:
- arteriosclerosis (R v Kemp [1957] 1 QB 399);
- epilepsy (R v Sullivan [1984] AC 156);
- hyperglycaemia in diabetes (R v Hennessy [1989] 1 WLR 287);
- sleepwalking (R v Burgess [1991] 2 QB 92).
An external cause – a blow to the head, or a drug taken on medical advice – is not a disease of the mind. That is the territory of non-insane automatism, which leads to an outright acquittal. A state brought on by voluntarily taking alcohol or drugs cannot found a defence of insanity (R v Coley [2013] EWCA Crim 223).
3. Not knowing the nature and quality of the act
This refers to the physical character of what the defendant was doing. The classic illustration is a defendant who, because of their condition, did not appreciate that they were strangling someone – believing, for example, that they were squeezing an object rather than a person’s neck.
4. Not knowing the act was wrong
“Wrong” means legally wrong. A defendant who knew their act was against the law is not insane within the Rules, even if their illness led them to believe it was morally justified (R v Windle [1952] 2 QB 826, confirmed in R v Johnson [2007] EWCA Crim 1978). This is one of the most criticised features of the Rules, because it excludes defendants whose delusions led them to believe they were doing right.
Delusions
The judges in M’Naghten also addressed the defendant who acts under a delusion but is otherwise sane. Such a defendant is judged as if the facts were as they believed them to be. If, under a delusion, they believed someone was about to kill them and killed in what they took to be self-defence, they would not be liable; but if the delusion was only that the victim had injured their reputation, and they killed in revenge, they would be. In practice, delusional cases are now usually argued within the main test or through diminished responsibility.
Proof and medical evidence
The burden of proving insanity lies on the defence, on the balance of probabilities. A jury may not return the special verdict except on the written or oral evidence of two or more registered medical practitioners, at least one approved under section 12 of the Mental Health Act 1983 (Criminal Procedure (Insanity and Unfitness to Plead) Act 1991, section 1). The decision remains the jury’s.
The special verdict and disposal
In the Crown Court the verdict is not guilty by reason of insanity (Trial of Lunatics Act 1883, section 2). Under section 5 of the Criminal Procedure (Insanity) Act 1964 the court must then make one of three orders:
- a hospital order, with or without a restriction order;
- a supervision order;
- an absolute discharge.
Where the charge is murder and the conditions for a hospital order are met, the order must be made with restrictions. The choice between the others depends heavily on the psychiatric evidence about treatment, risk and whether a hospital bed is available.
The magistrates’ court
Insanity is also available in summary proceedings, where a successful defence results in an acquittal. Separately, section 37(3) of the Mental Health Act 1983 allows a magistrates’ court to make a hospital order without convicting, if satisfied that the defendant did the act and the conditions for an order are met.
Criticism and reform
The Rules date from 1843 and are widely criticised. They focus on knowledge rather than on a defendant’s capacity to control their actions; they label conditions such as diabetes and epilepsy as diseases of the mind; and the narrow meaning of “wrong” excludes defendants whose illness led them to believe they were morally justified. The Law Commission examined insanity and automatism in a discussion paper in 2013, proposing a new defence based on a recognised medical condition, but the law has not changed.
What the psychiatric report addresses
An insanity report reconstructs the defendant’s mental state at the material time – often months earlier – from medical records, witness statements, the police interview and custody records, and the defendant’s own account. It addresses the diagnosis and its course; how the condition affected the defendant’s reasoning at the time; each element of the Rules in turn; the role of any intoxication; and alternative issues such as diminished responsibility, capacity to form intent and fitness to plead. Where the defence may succeed, it addresses the appropriate disposal and whether a hospital bed is available.