There have been many controversial debates on the defence

Insanity reform act burden of proof

The insanity defence reform Act 1984 has stated the burden of proof was shifted from the prosecution to the defence and the standard of evidence was increased from predominance of evidence to clear and convincing evidence. There is different standard of proof required for the defence of insanity, but this depends on who has raised the defence of insanity the defence or the prosecution. The difference is that the defence must prove on the balance of probabilities, and the prosecution must prove beyond reasonable doubt. This is most likely to confuse juries. It conflicts with the decision in the case of Woolmington v DPP (1953) which states that the burden is on the prosecution to prove the offence not the defence. The defendant has to prove that s/he was suffering from insanity when s/he committed the offence. This places the evidential burden on the defendant. Critics have argued that it is unfair that the evidential burden is on the defendant they claim that there is possibilities that Art 6 of the ECHR is in breach, which states that the defendant is innocent until proven guilty.

Mnaughten rules

The House of Lords established the M’Naghten rules in 1843, it defines the legal terminology of insanity. To establish the defence of insanity, the accused must satisfy the M’Naghten rules. This presents that an individual is presumed sane unless it can be proven that at the time of the offence he was “labouring under such defect of reason, arising from a disease of the mind, as not to know the nature and quality of the act he was doing, or if he did know that he did not know what he was doing was wrong."

Rules should be abolished because its old

The law on insanity is outdated and in need for urgent reform. The legal definition of insanity has not changed since 1842 and in 1953 evidence provided to the Royal Commission stated the definition of insanity was obsolete and misleading. The issue of insanity has been recognised by the law commission and they include insanity in the 10th programme of reform. They stated “The problems with the existing law are many and serious …and the current rules for determining legal insanity date from 1842.   In those days, the science of psychiatry was in its infancy." The law commission recommended the abolishment of the M’Naghten rules but this didn’t occur, instead Diminished Responsibility (DR) was introduced as a partial defence to murder.

Critics supported the defence of DR, as they believed it alleviate the uncertainties created by the insanity defence. The defence requires proof that the defendant was suffering from “abnormality of mind", which “substantially impaired" mental responsibility for their acts. DR is determined by the juries, the defence is open to be interpreted “in accordance with the morality of the case rather than the application of psychiatric concepts". However the defence of insanity and DR has a major flaw, as it allows juries to decide the verdict and the sympathy factor can play a part in mitigating the sentence, which deviates from the fundamental issue of criminal liability.

Legal rule not medical insanity

The rules for establishing insanity are entirely based upon legal formulas. Medical professions have criticised the law because the legal definition on insanity is ‘medically irrelevant’ it dates from 1843 and the courts do not take medical views on insanity into account. Smith and Hogan argue that the rules are about responsibility rather that insanity, The legal definition of insanity is only concerned with defect of reason and is not designed to take into account the developments of modern medical science. Due to the medical and legal advances it bears no relation to modern society. The Law Commission stated “the application of these antiquated rules is becoming increasingly difficult and artificial.  For example, the key concept of "disease of the mind" has no agreed psychiatric meaning".  Lord denning in rv bratty states “Any mental disorder which has manifested itself in violence and is prone to recur is a disease of the mind."

2 Doctors

The definition of “disease of the mind" is a very controversial issue. It is argued that according to the rules, it is a legal definition not medical. Under the criminal procedure (unfitness to plead) Act 1991 states the court must hear evidence of two medical practitioners who have experience in diagnosis of mental disorder, in order to establish the defence of insanity but this has now been overruled as the courts have continued to interpret the Rules to include within the definition states of mind that the medical profession would not classify as a “disease of the mind".

For example, in the case of Sullivan. Despite medical evidence asserting that a disease of the mind was a disorder of brain functions for a prolonged period of time and further asserting that a seizure was not a disease of the mind, this was held to be irrelevant. It was found that the defendant’s epilepsy had during the course of the actual seizure caused impairment of faculties, which in turn caused a defect of reason, thereby satisfying the legal definition of insanity.

The case Kemp stated the concept “disease of the mind" claiming it is any internal disorder affecting the ordinary faculties of reason, memory and understanding so that the condition of the brain was irrelevant. This approach is not always reconcilable with established medical expert opinion it further heightens uncertainty with regard to the level of mental disorder required to constitute insanity.

Rule is broad

However, critics have argued that the Rules are too broad people who are suffering from physical illnesses such as diabetes Hennessy, epilepsy Sullivan, heart disease Kemp, and sleep walking Burgess are extremely outraged to discover that the law labels them legally insane as their actions stem from an ‘internal cause’. This shows the law does not differentiate between people who is a danger to society and those who suffer from medical illnesses such as diabetes and epilepsy etc, the law fails to distinguish that these conditions can be controlled by medication.

It must add further pain to the accused when the result of a successful insanity plea is not a straightforward acquittal; it is the ‘special verdict’ of ‘not guilty by reason of insanity’ under the trial of Lunatics Act 1883. Surely it would not have been a difficult task for parliament to have repealed the act and modernised the law, rather than merely amending it in 1991.


On the other hand it could be argued that the definition insanity carries a social stigma. For murder charges D’s would be more likely to use the defence of DR. So therefore it is inappropriate to use it in relation to people who are suffering from mental disorders but it is completely unsuitable to apply insanity to those suffering from diseases such as epilepsy or diabetes. There have been situations where defendants have pleaded guilty when they are innocent to avoid being labelled as insane due to the stigma attached Clarke.


Another limiting factor to the insanity defence is that the “disease of the mind" must arise from an internal factor. In Quick, D committed an assault in a state of hypoglycaemia caused by the insulin he had taken, and the alcohol he had consumed and not eating. The Court of Appeal held that the defence of insanity was not available because the condition was caused by an external factor, it was not caused by “disease of the mind".  However, a distinction was drawn in Hennessy, where it was held that the condition was a symptom of diabetes, D failed to take his insulin and therefore the defence of insanity was available. However, this distinction seems flawed as it is an attempt to distinguish between conditions caused by a disease of the mind which may recur and pose a threat to the public.

Judges unhappy – development of insanity

The judges themselves are not satisfied with the development. In Quick Lawton LJ stated ‘common sense is affronted by the prospect of a diabetic being sent to such a hospital when in most cases the disordered mental condition can be rectified quickly by pushing a lump of sugar... into the patients mouth’. It is considered that too much sugar in the blood can be rectified quickly. Lord Lane in Burgess, Lord Diplock in Sullivan and both the trial judge had urged parliament to look into this matter, to give the judges further guidance.

Despite the policy reason for these decisions to protect the public interest from conditions resulting in a propensity to violent behaviour , there are many serious mental disorders that may not result in violence, yet would medically be considered to suffer from a disease of the mind. it seems absurd and unfair to label epileptics as dangerous compared with those suffering from psychosis for example.

Insanity treatment issues

This also highlights flaws in the legal defence of insanity and the criminal justice system, in failing to provide adequate social services necessary to deal effectively with mentally disordered offenders. Home Office Statistics demonstrate an increase in the number of offenders on early release from custody, along with an increase in the number of offenders subject to hospital orders under the Mental Health Act 1983 (“the Act"). If mentally disordered offenders are slipping the net and not receiving necessary treatment and care due to not satisfying the legal test of insanity, this clearly seems to be contrary to the public interest, which is the fundamental basis of the courts’ reasoning when determining insanity pleas.

Rule is narrow

This rule is very narrow because people, who suffer from certain mental disorders for instants irresistible impulse and psychopaths in the case of Byrne, cannot raise the defence of insanity. Because they know the nature and quality of their act or that it is legally wrong but is nonetheless unable to stop themselves from committing it. Thus, those at whom the defence should be aimed at are unable to rely on it. Section 2 Homicide Act 1957 the defence of Diminished responsibility (DR), recognise these types of condition, DR reduces the conviction of manslaughter with more discretion on the part of the judge in regards to sentencing. Lord denning in bratty states “when a man is charged with murder, and knew what he was doing and claims “i couldn’t help myself" is no defence in itself". Irresistible impulse may be evidence of DR byrne.

Nature and quality of act

Finally the defence of insanity is not available in ignorance of the law Windle held that a defendant who is suffering from a serious recognised mental illness and who does not know that his act is morally wrong cannot use a defence of insanity when he knows that his act is legally wrong confirmed in Jhonson. An Australian case refused to follow this decision. In Johnson the Court of Appeal thought that the Australian case had good points but recognised that they were obliged to follow Windle. This suggested that the law on insanity is long overdue and urgent review of the law is needed.

The word "wrong" should be interpreted to mean morally wrong. This issue attracts debate. Decision in Windle claims the word "wrong" in the M'Naghten Rules means legally wrong this has been supported judicially by Lord Devlin stating: “I do not see how an accused man can be heard to say that he knew he was doing an act which he knew to be contrary to law, and yet he is entitled to be acquitted at the hands of the law. Guilt, whether in relation to the M'Naghten Rules, or any other rules, means responsibility in law."

In any event, the "knowledge of wrong" interpreted in Windle provides a very narrow ground of exemption because even disturbed people generally know that murder, is a crime. It appeared that the judges had taken a generous approach in practice in establishing the ‘wrong’ test whilst directing juries and little attempt was made in many cases to distinguish between ignorance of legal wrong and ignorance of moral wrong.

Once the disease of the mind has been established, it must then be proven that it induced a defect of reason and the courts have interpreted this as a complete loss of power or reasoning and that the defendant does not know the nature and quality of his act . Again, this is very stringent and outside of medical opinion that even psychotics can appreciate the nature and quality of their acts.

This is further exasperated by the courts’ tendency to adopt a narrow interpretation of the requirement. In the case of Windle , it was asserted that the relevant test was whether the defendant knew that its actions were in breach of law. The issue of whether the defendant knew what they were doing was morally wrong was not held to be relevant. However, this leads to undesirable results. In Sutcliffe , the defendant was a schizophrenic, however had a clear knowledge and appreciation that his actions were contrary to the law and was therefore held not to be insane. This in itself would suggest that this is not a satisfactory test for criminal responsibility and surely not in the public interest where on the one hand schizophrenics may not be considered legally insane, yet the rules are stretched to cover diabetics and epileptics.

The danger in cases like the above is that a defendant clearly needs to be in care with the appropriate facilities yet is sentenced to a prison term, which raises the question as to whether mental disorder offenders should actually be diverted from the criminal justice system. Furthermore, in the event of conflicting medical evidence regarding mental disorder, juries are required to determine whether the defence of insanity or diminished responsibility can be used. This clearly raises concerns as to whether it is appropriate for inexperienced jurors to determine the complexities of mental disorder in the context of criminal responsibility.

Additionally, the criminal defence of insanity seems to be incompatible with the civil law position under the Act. The Rules have been stretched to cover epileptics and diabetics, a category that is highly unlikely to be committed under the Act, while omitting others that although not legally insane, would be committed according to established medical opinion. This highlights the fundamental issue of what actually constitutes a mental disorder for the purpose of determining legal criminal responsibility, which is clearly in a current state of confusion.

Sentencing procedure

Many criticisms can be made to the verdicts on insanity cases. The defence of insanity is rarely used, due to the strict sentencing procedure. If the defendant is found ‘guilty by reason of insanity’ then the judge would have no alternative but send him to an indefinite place in a secure hospital without a maximum sentence. In contrast, a conviction for murder or manslaughter would result in a determinate sentence of between 10 – 15 years. Most defendants would possibly prefer a straightforward conviction. It has been suggested that many defendants with mental problems do not raise the defence for these reasons and this means that such insane defendant are not receiving the treatment they need and instead are detained in prisons. There is also a potential conflict with Article 5 of the ECHR which states a person of unsound mind may only be detained where proper account is taken of objective medical evidence. There is likely to be a human rights challenge on indeterminate sentences. But, no cases have occurred in which this point has been argued.


the Butler Committee recommended that proof of severe mental disorder should be sufficient to negate responsibility, this would create a presumption of no criminal responsibility where ther is proof of a severe mental disorder. This has been criticized as it assumes a lack of criminal responsibility simply because there is evidence of some sort of mental dysfunction. According to this view, the law should be guided to responsibility not mere psychiatric diagnosis.

This has raised questions whether mental disorder offenders should actually be diverted from the criminal justice system, in order to be dealt with more effectively.


The Law Commission’s 10th programme of Law Reform includes a review of the insanity defence.

Given the vulnerability of the mentally ill and the increasing frequency with which they are coming into contact with the criminal justice system, modern criminal law should be informed by modern science, and in particular by modern psychiatric thinking.

The problems with the existing law are many and serious.  The current test for determining fitness to plead dates from 1836 and the current rules for determining legal insanity date from 1842.   In those days, the science of psychiatry was in its infancy.

The application of these antiquated rules is becoming increasingly difficult and artificial.  For example, the key concept of "disease of the mind" has no agreed psychiatric meaning.  As interpreted by the courts, it has even come to include conditions that are not mental disorders, such as epilepsy and diabetes.  The stringent test of capacity for the purposes of fitness to plead also needs to be reconsidered and should be contrasted with the much wider test contained in the Mental Capacity Act 2005.

The Criminal Law Revision Committee and the Committee on Mentally Abnormal Offenders 1975 (the Butler Committee) suggested a verdict of ‘not guilty on evidence of mental disorder’ to avoid the stigma of insanity. They suggested this defence could apply where there was evidence the accused was suffering from one of a range of mental illnesses or abnormalities when he committed the actus reus of the offence even though he showed no evidence of having formulated the mens rea of that offence.


The Butler Committee on Mentally Abnormal Offenders reported in 1975 that major reform was necessary. The Report recommended the introduction of a new verdict of "not guilty by reason of mental disorder" which could be returned in two situations: a) where the defendant was unable to form the requisite mens rea due to mental disorder; or

b) where the defendant was aware of his actions but was at the time suffering from severe mental disorder.

proposals for reform made by the Butler Committee. Clauses 35 and 36 of the draft code bill detail the two circumstances in which the proposed mental disorder verdict would be returned: (i) where all the elements of the offence are proved but the mental disorder nevertheless should result in an acquittal (corresponding to the "wrong" limb), and (ii) where the mental disorder precludes the required fault (corresponding to the "nature and quality" limb).

Clause 35 provides:

"(1) A mental disorder verdict shall be returned if the defendant is proved to have committed an offence but it is proved on the balance of probabilities (whether by the prosecution or by the defendant) that he was at the time suffering from severe mental illness or severe mental handicap.

(2) Subsection (1) does not apply if the court or jury is satisfied beyond reasonable doubt that the offence was not attributable to the severe mental illness or severe mental handicap."

Clause 36 seeks to provide for the defendant who, through mental disorder, acts without the requisite fault element. It states:

"A mental disorder verdict shall be returned if- (a) the defendant is acquitted of an offence only because, by reason of evidence of mental disorder or a combination of mental disorder and intoxication, it is found that he acted or may have acted in a state of automatism, or without the fault required for the offence, or believing that an exempting circumstance existed; and (b) it is proved on the balance of probabilities (whether by the prosecution or by the defendant) that he was suffering from mental disorder at the time of the act."