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Insanity: Evaluation & Reform

Study Note | A Level

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The defence of insanity has been criticised for many years and the need for reform seems to be generally accepted.

Dr Winstanley, set out his objections in a House of Commons debate in 1967:

.. These rules were formulated following the case of Daniel M'Naghten and they are still in force despite the fact that they have been almost constantly subjected to criticism and attack, not only by the medical profession but by lawyers and members of the general public.
I do not need to repeat the various attacks that have been made over the years, but it is interesting to note that as long ago as 1874 the noble Lord, Lord Bramwell, giving evidence to the Select Committee on the Homicide Law Amendment Bill in June, 1874, said that ‘the present law lays down such a definition of madness that nobody is hardly ever really mad enough to be within it’. That is the kind of view which has been held by the many people who have frequently criticised this form of the law. We had much criticism at the time of the Royal Commission on Capital Punishment, since when we have had a general acceptance of the fact that the M'Naghten Rules, while they provide a basis, do not necessarily provide a satisfactory one.
Briefly, the important rules - two of them; there are others which are less important today - provide that a person can only be found insane in relation to a criminal act if, first, he is unaware of the nature and quality of the act which he is doing, or, secondly, if he is so aware, that he is not aware that that particular act is wrong.
Many people have held that we should alter the law to embody provisions to cover the type of mental abnormality which could result in a person, while he was aware of what he was doing, or while he might be aware that what he was doing was wrong, was none the less subject to an uncontrollable impulse or otherwise unable to control his behaviour...


The definition is a legal not medical one, which raises some uncertainty.

It means some people suffering from certain mental disorders are excluded. Including those who may know what they are doing is wrong but have an irresistible urge to act in that way, for example, psychopaths (Byrne (1960)).

Conversely those suffering from some physical illnesses may be considered legally insane, for example diabetes (Hennessey (1989)).

Burden of proof

The shifting burden of proof depending on whether the prosecution or defence is arguing insanity is confusing and inconsistent and provides an added complication for a jury. It seems to conflict with the principle the burden lies with the prosecution.

Woolmington v DPP (1935)

Viscount Sankey: .. No matter what the charge or where the trial, the principle that the prosecution must prove the guilt of the prisoner is part of the common law of England and no attempt to whittle it down can be entertained....


The meaning of the verdict makes insanity a less favoured defence.

  • Indefinite detention

    A finding of insanity can lead to indefinite detention in a secure hospital, which can be a greater sentence than a life sentence with a tariff of 15 years.

    It is well documented that many offenders suffer mental health problems and yet insanity is a relatively uncommon defence, maybe partly because of the potential consequences.

    Under Article 5 of the European Convention on Human Rights a person of unsound mind may be detained but are also afforded protections, which have been interpreted to mean the need for objective medical expertise. Such expertise is not always involved in an insanity plea.

  • Stigma

    Much social stigma surrounds the term insanity. Some argue it is an outdated term and should not be applied to those suffering from mental illnesses. Indeed in cases involving people suffering from diabetes or epilepsy it seems a wholly inappropriate categorisation.


It has been recommended that proof of a severe mental disorder should be sufficient to negate responsibility. However, this would allow criminal responsibility to be determined by the presence of a mental problem rather than establishing a standard of criminal responsibility. This would raise the question as to whether the defence should be available for all crimes, even those not requiring mens rea.


The overlap between the defences is clear. The distinction lies in whether the defendant’s action is due to an automatic state induced by an illness or external factor.

However, the defences lead to very different verdicts and results. A person successfully arguing automatism is entitled to an acquittal but a verdict of not guilty by reason of insanity means the judge must impose some order.

Proposals for reform

On numerous occasions, studies have looked at the defence of insanity however, substantial reforms have yet to be enacted. More recently the Law Commission have begun a review of this area of the law which may eventually lead to considerable reform.

  • Royal Commission on Capital Punishment 1953

    The Commission found the M’Naghten Rules were inadequate and needed to be changed.

    The Commission criticised the test for responsibility and scope of the rules recommended that mental deficiency be considered a factor.

    The suggestions were not implemented the introduction of the partial defence of diminished responsibility addressed some of the criticisms.

  • Butler Committee 1975

    The Committee’s report on Mentally Abnormal Offenders stated that major reform was necessary.

    The main recommendation was the introduction of a new verdict of not guilty by reason of mental disorder. This could be applied where the defendant was unable to form the required mens rea due to mental disorder or was aware of his actions but was at the time suffering from a severe mental illness.

    It was suggested this defence may help alleviate the stigma of insanity.

  • Law Commission

    Under the Law Commission’s Tenth Programme of Reform , which commenced at the beginning of 2011, one area under consideration is Unfitness to plead and the insanity defence.

    In the document outlining the programme for reform the Law Commission discussed its intention to look at the defence of insanity.

    .. Those who are mentally ill are amongst the most vulnerable of society’s citizens. One would hope and expect that the rules governing the criminal liability of the mentally ill would be informed by humane principles while recognising the Government’s legitimate concern that the public should be adequately protected from harm...
    .. The link between crime, mental illness and intoxicants can be seen in our prisons where many inmates have a history of abuse of intoxicants combined with mental health problems...
    .. The problems with the current law are many and deep. They are not problems that exist merely at the margins. It was noted above that one would expect thelaw to be informed by modern psychiatric thinking. Yet, the current test for determining fitness to plead dates from 1836. The current rules for determining legal insanity date from 1842. In those days, the science of psychiatry was in its infancy...
    .. As well as the test for determining fitness to plead being antiquated, there are unanswered questions as to the scope of the trial of the facts following a finding of unfitness to plead...
    ..There are other fundamental issues that need to be addressed. One is the relationship between insanity and automatism. The relationship is unsatisfactory because of the ‘external factor’ doctrine...
    .. The relationship between insanity and the partial defence of diminished responsibility is also complex and needs to be re-evaluated...
    .. The area is highly suitable for a Law Commission project. The foundations of the current law rest on judicial rulings made in the first half of the nineteenth century. As a result, the legal tests consist of concepts on which there is no agreed psychiatric meaning. A finding of insanity attracts huge stigma and it is a finding which, under the current law, may be made in cases where the defendant was not mentally disordered...

    The consultation process is currently underway and recommendations from the Law Commission will provide suggestions for future reform.

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