When a defendant with a physical or mental incapacity commits a criminal offence, his criminal liability comes into a question. A defence of automatism may be open to such a defendant. The legal meaning of the defence of automatism has evolved to mean that the defendant's conduct was involuntary. In the case of Bratty  , Lord Denning regarded an act as involuntary when it is done "by the muscles without any control of the mind" or "by a person who is not conscious of what he is doing."
The law regarding automatism has now come to distinguish between "non-insane" and "insane" automatism, or automatism and insanity, respectively. For a successful plea in automatism, the law holds that the defendant must have suffered from a complete loss of voluntary control  due to an external factor  . The law on insanity dates back to the 1842 case of McNaghten  where it was established that a defendant must prove that he was labouring under a defect of reason from disease of the mind and did not know what he was doing was legally wrong.
Whilst a successful defence of automatism results in a complete acquittal, a successful defence of insanity results in a special verdict of not guilty by reason of insanity with the defendant facing certain constraints under a hospital order for the protection of the public.
The distinction between automatism and insanity hinges on whether the cause of the involuntary conduct was due to an external or internal factor. If the factor is internal, the plea is not guilty by reason of insanity; if external, the plea is not guilty.
There has been wide criticism of the common law defences of automatism and insanity with many proposals for reform raised. Indeed, Lawton LJ in Quick  acknowledged the need for guidance describing the defence as "a quagmire of law seldom entered nowadays, save by those in desperate need of some kind of defence". Notably, the Law Commission are currently reviewing the insanity defence  . Accordingly, this piece of work aims to consider and bring together the way in which defences are open to criticism and should be reformed.
This piece will look at the blurred line between the distinction of external and internal factors. It will focus on the antiquated McNaghten rules and whether they are compatible with modern medical understanding of mental incapacity. It will look at the effects of the burden of proof shifting to the defendant on pleading insanity and whether this is compatible with the ideal of an individual's right to a fair trial and the presumption of innocence. It will question whether hospital orders for indefinite periods of time are the correct redress for defendants found not guilty by reason of insanity. Lastly, it will examine evidence to suggest that some defendants preferred to plead guilty for a crime not committed in order to avoid an indefinite period of hospitalisation and the social stigma attached to being labelled "insane".
Distinguishing between external and internal factors
In general, conduct is regarded as involuntary but sane, if resulting from an external factor. Conduct is regarded as insane if it arises from an internal factor or disease and is therefore subject to recurrence. Justification for the distinction can be made on the ground that it is in the interests of public policy to identify those who can be safely acquitted and those who are dangerous so need restraint in the form of detention in a psychiatric hospital.
However, whilst this may be true of a comparison between a state of mind caused by an internal long-term mental illness, and one caused by an external factor such as a sudden blow to the head, the doctrine of distinguishing between external and internal factors has drawn much criticism as it has led to irrational distinctions such as that drawn from the cases of Hennessy  and Quick  .
Hennessy committed a crime whilst in a hyper-glycaemic state after neglecting his diabetes by failing to inject insulin. It was held that his diabetes, which caused the excessive blood sugar level and his hyper-glycaemic state, was an internal factor that could recur at any time. He was therefore found not guilty by reason of insanity under the McNaghten rules and became the subject of a hospital order.
On the other hand, Quick was a diabetic who had eaten insufficient food to counter-balance the insulin he had administered leading to him committing an offence during a hypo-glycaemic state. Lawton LJ said:
"In this case Quick's alleged mental condition, if it ever existed, was not caused by his diabetes but by his use of the insulin prescribed by his doctor. Such malfunctioning of his mind as there was, was caused by an external factor and not by a bodily disorder in the nature of a disease which disturbed the working of his mind."
It was held that a malfunctioning of the mind caused by the application of an external factor (in Quick's case, this was insulin) is not a "disease of the mind" and would lead to a complete acquittal.
Cases involving defendants suffering from diabetes provide good examples of the problems of the internal/external divide doctrine established in Quick. Not only is it absurd to label a diabetic insane but both defendants may have acted with the same state of mind but each obtain a very different verdict.
As stated above, the rules governing the defence of insanity date back to the McNaghten case in 1842. Under the rules the defendant must be labouring under "a defect of reason, from 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".
The subsequent interpretation of "disease of the mind" has led to much criticism. Under the McNaghten rules, the definition is a legal one, not medical. Consequently, submitted evidence of two medical experts in order to establish insanity (required under the Criminal Procedure (Unfitness to Plead) Act 1991  , has been overruled by courts continuing to interpret insanity under the McNaghten legal definition. The legal definition of "disease of the mind" does not sit well with the medical profession as a "disease of the mind". For example, in Sullivan  which concerned the defendant kicking out a friend during an epileptic seizure and where the defendant had produced medical evidence to suggest that epilepsy was not a "disease of the mind", Lord Diplock held that only where temporary impairment resulting from an external factor, such as a blow to the head, will the epileptic attack not be attributed to a disease of the mind.
Professor Glanville Williams believes Sullivan has "vastly" extended the legal concept of "disease of the mind" which is of "great concern to sufferers from epilepsy" which is "capable of having wider implications" 
In the case of Kemp  , who was a defendant suffering from arteriosclerosis, where hardening of blood in the arteries prevents oxygen from reaching the brain, it was held that "disease of the mind" meant any internal disorder affecting the defendant's reasoning. Although he again produced two medical expert opinions to show he was not suffering from a "disease of the mind" under the medical definition, the court found him not guilty but by reason of insanity.
The approach by the courts to the definition of "disease of the mind" does not sit well with medical expert opinion. As seen in the cases above, this has led to defendants suffering from diabetes, epilepsy, arteriosclerosis and sleepwalking (as per Burgess  ) unjustly and absurdly being labelled as insane.
Furthermore, complaints have arisen with regard to a possible breach of Article 5 of European Convention on Human Rights - the right to liberty/security of person. Defendants have been deprived of their liberty because of mental health reasons based on the archaic McNaghten rules predating the European Convention on Human Rights.
Burden of Proof
On pleading "insanity" the burden of proof shifts to the defendant  , albeit on the balance of probabilities. This is in comparison with other defences, including automatism, where the burden of proof beyond all reasonable doubt rests with the prosecution in the normal way. Questions have been raised as to the compatibility with this shift of the burden of proof to the defendant with the human right of the presumption of innocence  .
Certainly there is an example of an application to the European Commission of Human Rights regarding this issue  where the applicant complained that the burden of proof on him to show, on the balance of probabilities, that he was suffering from a defect of reason, did not comply with the presumption of innocence ensured by Art 6(2) of the Convention. He argued that the McNaghten rules imposed an unjustifiable burden on him. The application was found to be inadmissible but it does show that questions have already and will continue to be raised regarding the shift of the burden of proof to the defendant.
Further on this point, it was established in Woolmington  that there is a presumption of innocence of the defendant and the onus is on the prosecution to prove beyond all reasonable doubt that the defendant is guilty. However, Viscount Sankey LC did distinguish insanity as an exception to this rule stating that "in M'Naughton's case, the onus is definitely and exceptionally upon the accused to establish such a defence".
It is argued that Viscout Sankey's approach is questionable  . Jones states that "it is doubtful that the judges in the M'Naghten case would have taken the view that they were "definitely and exceptionally" placing the burden of proof on the accused".
Also noted by Jones is that "there is considerable scope for confusion (and judicial error) in this area of law. In a trial where insanity is a live issue there are two different burdens: that of the prosecution to provide the elements of the offence beyond all reasonable doubt; and that of the accused to establish insanity on the balance of probabilities". 
Hospital Orders and Social Stigma
The label of "insane" attached to someone found not guilty by reason of insanity is questionable.
Lastly, there is evidence of an ineffectiveness of the verdict of insanity. Where faced with an indefinite hospital order and fixed with the "insanity" label or a definite custodial sentence, some defendants have pleaded guilty for a crime they did not commit.
Evidence showing defendants change their plea to guilty of non-insane automatism not available - Hennessy and Sullivan
In 1975 the Butler Committee recommended the introduction of a new verdict of not guilty by reason of mental disorder  which should be available where the defendant was unable to form the necessary mens rea due to mental disorder or where the defendant was aware of his actions but was suffering from a mental disorder at the time.
Whilst the proposals by the Butler Committee may widen the scope of the defence to include the severely mentally ill, its proposals do not remove the stigma of the mental illness defence.
The draft Criminal Code Bill which the Law Commission is still working on, does incorporate some of the recommendations by the Butler Committee.
The Criminal Procedure (Insanity and Unfitness to Plead) Act 1991 contains provisions to allow the courts, when faced with defendants that have verdict of not guilty by reason of insanity, to have more flexibility when making hospital orders.