A2 - Law - The defence of insanity

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  • Created by: jkav
  • Created on: 15-06-16 20:48

The defence of insanity

Insanity as a defence is relevant only at the time the offence was committed. Insanity after that is only relevance is deciding whether the defendant stands trial or not. The defendant must prove that, on the balance of probabilities, he was insane at the time of the offence. If the prosecution wishes to raise the issue of the defendant's insanity, it must prove that beyond reasonable doubt. This is because evryone is presumed to be sane.

If the defence is found to exist, the defendant is not found 'not guility', but a special verdict of 'not guility by reason of insanity' is given. Under the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991 the court has a range of options available. For the offence of murder, the court must make a hospital order restricting the defendant's discharge indefinitely. For any other offence, the court may make one of the following orders:

  • a hospital order and an order restricting discharge either for a limited or unlimited period of time.
  • a guardship order
  • a supervision and treatment order
  • an order for absolute discharge

The law relating to the defence of insanity comes from the case of M'Naghten (1843). This case involved the attempted assassination of the then Prime Minister, Sir Robert Peel. The defendant missed but killed Peel's secretary, Edward Drummond. Medical opinion suggested the defendant was mentally ill, and this resulted in the House of Lords setting out rules for use in such cases.

The rules were set out in the case as follows:

'That if the accused was conscious that the act was one which he ought not to do; and if the act was at the same time contrary to law, he is punishable. In all cases of this kind the jurors ought to be told that every man is presumed to be sane, and to possess a sufficient degree of reason to be responsible for his crimes, until the contrary be proved to their satisfaction: and that to establish a defence on the ground of insanity, it must be clearly proved that at the time of committing the act the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing, or as not to know that what he was doing was wrong.

This sets out three key issues that must be established for the defence to succeed:

  • defect of reason
  • caused by disease of the mind
  • so that the defendant does not know the nature and qaulity of his act or does not know that what he is doing was wrong.

Defect of reason

The concept of defect of reason is based on an inability by the defendant to use powers of reason, rather tha his failing to use his powers of reason. Thus, a person who is confused or absent minded is not insane and, indeed, may have a defence to a crime…


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