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This defence is also known as insane automatism, and whilst it is concerned with the mental capacity of D, the concept is given a purely legal definition. As a result, it has been held to include conditions such as sleep walking, epilepsy and diabetes.

This defence is rarely used (perhaps 2/3 times per year) as its importance has been greatly reduced, particularly in murder cases, by two developments:

  • 1. The introduction of diminished responsibility by the HA 1957 (CAJA 2009).
  • 2. The abolition of the death penalty.

Insanity is a general defence available to all crimes which require proof of mens rea. It is not therefore a defence to strict liability.

DPP v H [1997] D suffered from manic depressive psychosis, but to a strict liability charge of drunk driving, he had no defence.

It is closely linked with AUTOMATISM, and is sometimes referred to as “insane automatism”. Although each of these may outwardly produce similar behaviour in the D, insanity is caused by an internal trigger and automatism by an external trigger.

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Often D does not specifically raise this defence, but will place his state of mind in issue by raising another defence, usually automatism or diminished responsibility. Therefore, it is most often suggested by the prosecution, or even the judge who will leave it to the jury for consideration. The prosecution must still have proven that D performed the AR but not the MR for the crime as Ds state of mind is only relevant to the issue of insanity.

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The Special Verdict

If D is deemed to have been insane at the time of performing the AR then the jury should return “not guilty by reason of insanity”: the special verdict (s.1 Criminal Procedure (Insanity) Act 1964). This is also known as a qualified acquittal.

Until recently, the special verdict obliged the judge to order D be detained indefinitely in a mental hospital. Consequently, once the death penalty was abolished, the dual prospect of the insanity label and indefinite detention discouraged Ds from putting their mental state at issue, leading to many guilty pleas to offences of which Ds were probably innocent as the punishment was unlikely to be worse than being locked away in a mental hospital with no fixed date for release (Quick [1973], Sullivan [1984] and Hennessey [1989]).

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This Act altered the sentencing obligation upon judges. In adding a new s.5 into Criminal Procedure (Insanity) Act 1964, a judge now has considerable discretion with regards sentencing following a special verdict. This section has recently been amended by the Domestic Violence, Crime and Victims Act 2004 and now allows the judge to make either:

  •  A hospital order (with or without a restriction order).
  •  A supervision order.
  •  An order for Ds absolute discharge.

This is particularly useful where the offence is relatively trivial and/or D does not actually require hospitalisation.

Such discretion does not however apply to murder cases. INDEFINITE HOSPITALISATION IS STILL UNAVOIDABLE. However, nowadays, Ds charged with murder are actually more likely to plead DR under s.2 Homicide Act 1957 (as amended by the s.52 CAJA 2009). Though these sentencing options have helped make insanity a more attractive defence, no attempt has been made to tackle the definition of insanity and so the ‘insanity stigma’ remains.

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THE M’NAGHTEN RULES: The law on insanity was laid

M’Naghten [1843] HL~D suffered extreme paranoia and thought he was being persecuted by the Tories. He was obsessed with PM, Sir Robert Peel. The PM’s private secretary, Edward Drummond (V), was walking towards Downing Street when D approached him from behind,and fired at point blank range into his back. It is generally thought that D believed he had shot the PM. D was found not guilty by reason of insanity and this produced enormous media and public disapproval that D could be ‘acquitted’ which prompted the Lords to answer some Qs concerning insanity in order to clarify the situation.

M’Naghten rules: “The jurors ought to be told in all cases that every man is PRESUMED TO BE SANE, and to possess a sufficient degree of reason to be held responsible for his crimes, until the contrary be proved......  There are 3 distinct elements:

  • 1. Defect of reason
  • 2. Disease of the mind
  • 3. Not knowing what D was doing or not knowing that it was ‘wrong’

If these elements are proven, they will rebut the presumption of sanity. Because of this presumption of sanity, the burden of disproving it is on the defence (on the balance of probabilities/reverse onus.)

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This means that Ds power of reasoning or ability to reason is impaired. D must be deprived of the power of reasoning, rather than simply failing to use such powers.

R v Clarke [1972]

D went into supermarket, placed various items (including butter, coffee and mincemeat) into her own bag and left without paying. She denied having formed the MR for theft (intention to permanently deprive) on the basis of a short period of absentmindedness caused by her mild depression. She claimed to have no recollection of putting items in her bag and the trial judge ruled that this was suggested insanity at which point D pleaded guilty (as to avoid mandatory detention in hospital). D then appealed against her conviction arguing that the judge was wrong to suggest insanity.

CA: Quashed her conviction as she was not insane; she simply lacked the MR for the crime, so the judge was incorrect to leave it to jury. They held that “defect of reason” applied only to “persons who by reason of a ‘disease of the mind’ are deprived of the power of reasoning.” It does not apply to people who simply have moments of confusion/absent mindedness.

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Insanity therefore requires an inability to exercise reason rather than a failure to do so.

 ABILITY TO REASON: rational thinking, controlled behaviour.

 INABILITY TO REASON: irrationality, strange or abnormal thoughts/behaviour.


R v Sullivan [1984] D was regarded as suffering a “defect of reason” when he suffered an epileptic fit and attacked a neighbour.

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Judicial interpretation makes this a LEGAL definition, not medical; therefore they will not always match.  The disease can be mental or physical and means a malfunctioning of the mind and includes: arteriosclerosis, epilepsy, diabetes and sleepwalking.

R v Kemp [1957] QB

D had arteriosclerosis (hardening of the arteries) which restricted blood flow to the brain and caused blackouts. During a blackout, D hit his wife with a hammer and was charged with s.20 OAPA 1861. This was clearly a physical, rather than mental condition and whilst D admitted he was suffering from a ‘defect of reason’ he said it was not due to a ‘disease of the mind’ as it was a physical problem, not a mental illness.

A special verdict of “not guilty by reason of insanity” followed (so insanity was successful proven) and he appealed against this. This was upheld by the CA who stated that the law was not concerned with the brain but with the mind.

Therefore, suffering from a condition which affects your ‘mental faculties’ amounts to insanity, which includes epilepsy.

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R v Sullivan [1984] D had suffered epilepsy since childhood. He was known to have fits and to show aggression towards those trying to help him during a fit. He injured an 80 year old man and the trial judge ruled this supported insanity and directed the jury as such. D then pleaded guilty to avoid hospitalisation, and then appealed. CA and HL confirmed the conviction as a plea of insanity was correct in the circumstances and so no there was no reason to quash his conviction as there had been no misdirection. Thus, if D suffers a condition affecting mental faculties, even temporarily, this amounts to insanity. The problem with this is how to distinguish such cases from situations when D suffers some temporary condition, such as concussion following a blow to the head. D loses his ‘mental faculties’ in the same manner but the problem is extremely unlikely to repeat itself and so ordering hospitalisation is pointless. In these cases the correct defence is actually (sane) automatism. In order to distinguish, the courts look at the cause of the “defect of reason” and ask was it INTERNAL or EXTERNAL? INTERNAL = INSANITY                                          EXTERNAL = AUTOMATISM

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Diabetes, a disease which is in no medical sense a disease of the brain, has been treated as legal insanity. It affects the body’s ability to use sugar and is usually controlled by injections of insulin, the substance which the body uses to break down the sugar.

Problems can arise where diabetics either:

  •  Fail to take their insulin, causing high blood sugar (hyperglycaemia) or
  •  Take the insulin and fail to eat when they should; causing low blood sugar (hypoglycaemia).

Either situation may lead the diabetic to behave aggressively but the laws approach has been rather odd.

  •  Hyperglycaemic episodes are treated as insanity because they are caused by the internal factor (the diabetes itself).
  •  Hypoglycaemia is regarded as sane automatism, because it is caused by an external factor (the insulin overdose).
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R v Quick [1973] D was a diabetic who had taken prescribed insulin to control blood sugar levels, which can affect the brain. He forgot to eat afterwards and subsequently suffered HYPOGLYCAEMIA (low blood sugar). Whilst in this condition, D (a nurse at a mental hospital) physically assaulted a patient. He could not remember what happened and the judge said this supported insanity.

At this point D pleaded guilty and then appealed. CA: Quashed the conviction as the cause of his lack of awareness was not diabetes (internal), but the insulin overdose (external) and therefore the proper defence was AUTOMATISM, which led to a full acquittal.

Lawton LJ: “Our task has been to decide what the law…means by the words ‘disease of the mind’… the fundamental concept is of a malfunctioning of the mind caused by disease. A malfunctioning…of transitory effect caused by the application to the body of some external factor such as violence, drugs, including anaesthetics, alcohol and hypnotic influences CANNOT fairly be said to be due to disease."

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The implications of this decision have been profound, and not without criticism and should be contrasted with:

R v Hennessy [1989]

D was a diabetic who had forgotten to take his insulin for 3 days due to stress and depression and suffered HYPERGLYCAEMIA (high blood sugar). During this time he was seen by police driving a stolen car and was charged with taking a vehicle without consent and driving whilst disqualified. D could not remember taking/driving the car, to which the judge declared that to be evidence supporting insanity. D changed his plea to guilty and appealed.

CA: In distinguishing from Quick the CA confirmed that HYPERGLYCAEMIA was internally caused by the diabetes and therefore a disease of the mind. Ds appeal was dismissed as the correct verdict was insanity. His guilty plea therefore remained.



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Two criticisms of diabetes disease of the mind

1. The relatively common medical condition of diabetes is regarded by the criminal law as supporting a defence of insanity, with all the negative implications that that label conveys.


2. This is only the case in certain situations namely where D suffers hyperglycaemia (high blood sugar).

According to Diabetes UK website, over 2.6 million people in UK have diabetes, and another 1/2 million are estimated to have condition without realising. Does the decision in Hennessey [1989] mean that over 3 million people in UK are (potentially) legally insane?!

Remember also that according to the HL, epileptics who have a seizure and inadvertently commit an offence are also to be regarded as insane. In R v Sullivan [1984] both the CA and HL said epilepsy was a disease of the mind as during a fit, mental faculties are impaired. According in Epilepsy Action website, 456,000 people in the UK have epilepsy (1 in 131 people). Should any one of these commit the AR of a crime during a fit, are they to be regarded as legally insane too?

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What about someone who carries out the AR of a crime whilst sleepwalking? This was the question in R v Burgess [1991] and despite persuasive precedent for deciding that it should amount to automatism, the CA held that it had to be regarded as insanity.

R v Burgess [1991] D and (girlfriend) V were watching videos in D’s flat. Both fell asleep but during the night, D attacked V while she slept hitting her on the head with a bottle. Before she could stop him, he had picked up the video recorder and brought it down on her head and he then grabbed at her throat. She cried out and D seemed to ‘come to his senses’, showing considerable distress at what he had done. D pleaded AUTOMATISM but trial judge ruled that as there was no evidence of any external cause for sleepwalking as a doctor had given evidence that it was due to a sleep disorder. The jury returned the special verdict of “not guilty by reason of insanity” and D was ordered to be detained in a secure hospital.

CA: Dismissed Ds appeal and upheld the special verdict.

Lord Lane CJ: “Sleepwalking was an abnormality or disorder, albeit transitory, due to an internal factor” and “we accept that sleep is a normal condition, but the evidence in the present case indicates that sleepwalking, and particularly violence in sleep, is not normal.”

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Parks [1992]

D killed whilst asleep and the court allowed automatism as the defence. Medical evidence was heard that sleepwalking was not regarded as a neurological, psychiatric or any other illness, but a sleep disorder found in 2-2.5% of adults. Furthermore, aggression while sleepwalking was quite rare, and repitition of violence almost unheard of.

**See case of Brian Thomas who killed his wife while dreaming. (BBC Article).**

To summarise the law on disease of the mind, the following conditions have been held to suport a plea of insanity in England & Wales:

 Arteriosclerosis – Kemp [1957]

 Epilepsy – Sullivan [1984]

 Hyperglycaemia (high blood sugar) – Hennessey [1989]

 Sleepwalking – Burgess [1991]

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What all of the ‘insanity’ conditions have in common is that courts consider them to be caused by an internal factor. Since they are internal, there is a risk they may reoccur, making the D a continuing danger to the public. The courts therefore prefer to label Ds insane and detained in hospital where necessary, rather than allowing a full acquittal under automatism.

R v Sullivan [1984]

“The purpose of the…defence of insanity… has been to protect society against the recurrence of the dangerous conduct.”

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It has also been suggested that the disease of the mind may need to manifest itself in violence in order to ‘qualify’.

Bratty [1963] D killed a girl during a mental blackout said to be due to psychomotor epilepsy, a disease of the nervous system.

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. At any rate it is the sort of disease for which a person should be detained in hospital rather than be given an unqualified acquittal.” Thus, it is suggested that some mental disorders which do not manifest themselves in violence, such as kleptomania (compulsion to steal) are not diseases of the mind for the purposes of insanity.

However, Denning’s statement that the mental disorder must be “prone to recur” was not followed in Burgess [1991] by Lord Lane CJ. The expert evidence in this case was that there was no reported incident of a sleep-walker being repeatedly violent. As Lord Lane concluded that the mental disorder need not be ‘prone to recur’, Burgess still fell within the definition of insanity.

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Nature and Quality of the Act

It seems D will have a defence provided that when D acted he was not aware of, or did not appreciate, what he was actually doing, or the circumstances in which he was acting, or the consequences of his act. Ds lack of knowledge must be fundamental (i.e. go to the core of the incident). This can happen because D is in a state of unconsciousness / impaired consciousness, or because of a mental condition D does not understand what he is doing.

In these D does not know what he is doing and so entitled to the special verdict but if D kills V, whom he believes, because of a paranoid delusion, to be possessed by demons he is still criminally liable and not insane as his delusion has not prevented him from understanding that he is committing murder.

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Where D knows the nature and quality of the act, insanity might still be available if D does not know that what he did was wrong. Does ‘wrong’ mean contrary to the criminal law or morally unacceptable or both? In M’Naghten the Lords said that if D knew he was acting contrary to law then he would not have a defence, even if D had a disease of the mind. This clearly suggests that D will have a defence if he does not realise he is committing a crime.

Windle [1952] D’s wife spoke often of committing suicide. One day, D killed his wife with an overdose of aspirin. When giving himself up to police, he said “I suppose they will hang me for this.” Despite medical evidence he was suffering from mental illness (folie à deux), his words demonstrated he clearly knew that what he did was legally wrong (but presumably thought he was morally right). D was convicted of murder, no special verdict and he was hung.

Lord Goddard CJ: “Courts of law can only distinguish between that which is in accordance with law and that which is contrary to law...The law cannot embark on the question … whether some particular act was morally right or wrong...There is no doubt that in the M’Naghten Rules ‘wrong’ means contrary to the law, and does not have some vague meaning which may vary according to the opinion of one man or of a number of people on the question of whether a particular act might or might not be justified.”

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This Windle 1952 position was criticised in 1975 in the Royal Commission on Mentally Abnormal Offenders (Butler Committee) which stated that the Windle definition of ‘wrong’ was a “very narrow ground on exemption since even persons who are grossly disturbed generally know that murder, for instance, is a crime.”

In Johnson [2007], the CA was invited to reconsider the decision of Windle. However, although the court agreed that the decision was ‘strict’, they felt unable to depart from it, believing that, if the law was to be changed, it should be done by Parliament.

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R v Johnson [2007] D suffered from delusions and auditory hallucinations (false perception of sounds). One day, armed with a large kitchen knife, he forced his way into a neighbour’s flat and stabbed him 4 times (V recovered). D was assessed by 2 psychiatrists who diagnosed him as suffering from paranoid schizophrenia. They agreed that D knew that his actions were against the law, however one was of the view that D did not consider that what he had done was morally wrong. The trial judge declined to leave insanity to the jury and D was convicted of wounding with intent (s.18 OAPA 1861) as knowledge that his acts were wrong in law was sufficient whatever Ds view as to the moral rightness or wrongness of his acts. CA upheld Ds conviction.

Latham LJ:“The strict position at the moment remains as stated in Windle...This area, however, is a notorious area for debate and quite rightly so. There is room for reconsideration of rules and, in particular, rules which have their genesis (origins) in the early years of the 19th century. But it does not seem to us that that debate is a debate which can properly take place before us at the level in this case.”

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In the Johnson 2007 judgement however, the CA pointed out an Australian case Stapleton [1952] where the court had refused to follow Windle [1952] as in their view, ‘morality’ and not ‘legality’ was the concept behind ‘wrong’.

Therefore, if D believed his act to be right according to the ordinary standard of reasonable men, then he was entitled to be acquitted even if he knew that it was legally wrong. The CA felt obliged to follow Windle [1952] but did express the opinion that Stapleton [1952] 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 [1952] is correct.”

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