Introduction

Insanity is only relevant at the time of the offence. A defendant must prove, on the balance of probabilities, he was insane at the time of the offence. There is a presumption of sanity, so the prosecution, if they wish to raise insanity, must prove a defendant insane beyond a reasonable doubt.

The defence of insanity is available for all offences were mens rea is required and therefore is excluded from strict liability offences.

If the defence of insanity is successfully argued then a special verdict of not guilty by reason of insanity is given. The judge will then make an appropriate order, depending on the defendant’s mental state. There are a range available including detention in a hospital, a guardianship order, a supervision and treatment order or an absolute discharge (Criminal Procedure (Insanity and Unfitness to Plead) Act 1991).

M’Naghten rules

The law relating to the defence of insanity is derived from a specific case.

Effectively, the ruling requires three elements to be proved. There must be a defect of reason. This needs to be the result of a disease of the mind. This must cause the defendant not to know the nature and quality of his act or not to know what he was doing was wrong. These are known as the M’Naghten rules.

Defect of reason

Defect of reasoning means a defendant’s powers of reasoning must be impaired. It is based on an inability to use powers of reasoning not merely a failure to do so.

Temporary confusion or absent mindedness does not amount to a defect of reason.

Disease of the mind

The term disease of the mind is a legal not a medical one. The law is concerned with the specific question of whether a defendant can be held liable for his act and not his medical condition. The disease of mind must be a physical one, not brought on by external factors, such as drugs.

There is no express definition but case law has developed some aspects of the meaning of disease of the mind.

• Temporary

  Kemp (1957)

  Defendant, during a blackout, attacked his wife with a hammer causing her grievous bodily harm. Medical evidence showed that he suffered from arterialsclerosis, a condition which restricted the flow of blood to the brain and caused temporary lapses of consciousness.

  The court found this was insanity not automatism. It was held that there was no distinction between diseases of the mind and diseases of the body affecting the operation of the mind. Also whether a condition was permanent was irrelevant.

  Devlin: .. In my judgment the condition of the brain is irrelevant and so is the question of whether the condition of the mind is curable or incurable, transitory or permanent. There is no warrant for introducing those considerations into the definition in the M’Naghten Rules. Temporary insanity is sufficient to satisfy them. It does not matter whether it is incurable and permanent or not....

• Source of disease

  Sullivan (1984)

  Defendant was charged with inflicting grievous bodily harm following an attack on his friend. Medical evidence showed he was epileptic and was having an epileptic seizure when the injury was caused and defendant argued automatism. The trial judge ruled he would direct the jury to return a verdict of not guilty by reason of insanity so the defendant changed his plea to guilty of the lesser offence of assault occasioning actual bodily harm. Defendant then appealed against his conviction.

  Court of Appeal and House of Lords confirmed the conviction. The source of the disease was found to be irrelevant.

  Lord Diplock: .. If the effect of a disease is to impair these faculties so severely as to have either of the consequences referred to in the latter part of the rules, it matters not whether the aetiology of the impairment is organic, as in epilepsy, or functional, or whether the impairment itself is permanent or is transient and intermittent, provided that it subsisted at the time of commission of the act....

• Reoccurring violence

  Bratty (1963)

  Defendant strangled the female victim in his car. Medical evidence showed he suffered from a psychomotor epileptic seizure at the time of the killing. The condition means someone can carry out a purposeful act whilst in an unconscious state.

  The court found this type of seizure could amount to insanity and provided a distinction between insanity and automatism.

  Lord Denning: ..It seems to me that any mental disorder which has manifested itself in violence and is prone to recur is a disease of the mind....

• Sleep walking

  Burgess (1991)

  Defendant wounded the victim, a friend, when sleepwalking. Medical evidence suggested the defendant suffered from a sleep disorder and there was no evidence of an external cause for the sleep walking.

  The trial judge ruled there was evidence sufficient for a finding of not guilty by reason of insanity and the Court of Appeal upheld this decision.

Defendant’s knowledge

Under the M’Naghten rules the defendant’s disease of mind must cause him not to know the nature and quality of his act or not to know what he was doing was wrong.

• Nature and quality

  The term nature and quality refers to the physical character of the act.

  Defendant can argue he did know the nature and quality of his act if he can prove that he did not know what he was doing or appreciate the consequences or appreciate the circumstances in which he was acting.

  If a defendant can prove he did not know the nature and quality of his act then he lacks sufficient mens rea. In these cases a verdict of not guilty by reason of insanity is given, rather than an acquittal.

• Wrong

  A defendant may know the nature and quality of his act but not realise it is wrong. Effectively, a defendant may have the necessary mens rea but because of his insanity he may not realise it was wrong. In these cases a defendant can still use the defence of insanity.

  Codere (1916)

  Defendant murdered his wife by cutting her throat, thinking it was a loaf of bread. Defendant argued insanity. It was found he was not able to rely on the defence of insanity because at the time he knew that it was unlawful to kill.

  Lord Reading: .. If the accused does know either that his act is morally wrong according to the ordinary standard adopted by reasonable men or that it is legally wrong then it cannot be said that he does not know he was doing what was wrong....

  Windle (1952)

  Defendant killed the victim, his wife, by giving her 100 painkillers. Victim had often spoken of her wish to commit suicide and was suffering from a mental illness. Defendant gave himself up to the police stating.. I suppose they will hang me for this.... Defendant argued insanity but his statement suggested he understood the nature and quality of his act and realised it was wrong.

  Insanity was not accepted as a defence. The word wrong means contrary to the law. The partial defence of diminished responsibility may be raised today in such a case.

  Johnson (2007)

  Defendant stabbed the victim, a neighbour, after forcing his way into his flat. Medical evidence stated he was suffering from paranoid schizophrenia and hallucinations. The two expert psychiatrists agreed he knew the nature and quality of his act and that it was legally wrong. One psychiatrist stated the defendant did not consider his act morally wrong. The judge ruled the defence of insanity was not available to the defendant. Defendant was found guilty of wounding with intent.

  Court of Appeal upheld the ruling that insanity was not available. The court was obliged to follow the decision in Windle (1952), that wrong means legal wrong.

  However, the court noted an Australian decision which found that a defendant could be acquitted even if he knew his act was legally wrong, but believed his act to be morally right. The court stated the Australian case contained .. illuminating passages indicating the difficulties and internal inconsistencies which can arise from the application of the M’Naghten rules if the decision in Windle is correct....

  Therefore, the definition of wrong is currently legal wrong but may be developed through future case law.