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Results in complete acquittal: an involuntary action must come from an external factor e.g. sneezing Whoolley [unreported]; PTSD R v T . The requirements of the defence are:
1. There must exist an involuntary action arising from external source or reflex action
2. The action must be completely involuntary
3. The automatism must not be self-induced. Therefore anything arising from inside the defendant will be insane automatism. Diabetes: if you have low blood sugar (take insulin but don't eat) and get hypoglycaemic it is non-insane. If you excessive blood sugars (failing to take insulin) and become hyperglycaemic, is is insane automatism.
Returns 'not-guilty by reason of insanity' which leaves the defendant at the disposal of the courts. The criminal justice system is failing for those with mental disorders, there is a high number in prisons; lack of treatment; lack of sufficient social policy. There are 2 situations where the mental condition of D will postpone or terminate legal proceedings before the trial:
1. Removal to a mental hospital - on the basis on reports by at least 2 medical professionals that D is suffering from a severe mental illness.
2. Unfit to plead - s.4 and 4A of the Criminal Procedure (Insanity) Act 1964 may mean that D is unfit to plead. The test of unfitness is left to the courts, it is whether D is "of sufficient intellect to comprehend the course of the proceedings in the trial so as to make a proper defence, to challenge a juror to whom he may wish to object and comprehend the details of the evidence" This is a dangerously narrow cognitive test and leads to decisions like Moyle
 where D had paranoid delusions and believed the court, his lawyers and the jury were involved in a conspiracy against him. The CoA refused to budge on its test and he was held fit to plead. The M'Naughten Rules - insanity defence is based on these rules, created by M'Naughten  where D killed Sir Edmund Drummond in an attempt to kill Sir Robert Peel. The rules provide that:
5 i. there is a rebuttal presumption that everyone is sane ii. proof of insanity requires proof of a defect of reason iii. the defect must emanate from some disease of the mind iv. it must be proved that the defect of reason either: (a) caused D to be unaware of the nature or quality of his act (b) caused D to not know that his act was wrong. i. Burden of proof - requires D to prove his insanity, which is discharged on the balance of probabilities. D has to produce some evidence to raise the issue of insanity - a verdict of not guilty by insanity will not be returned when evidence has been given by at least 2 medical practitioners including one specialist in mental health. ii. Defect of reason - failure of rationality; moral responsibility for the crime is absent. For the purposes of the insanity defence, the defect of reason may arise for a brief period and not need to constitute any aspect of D's character e.g. a temporary blackout. iii. Disease of the mind - not a medical question e.g. Kemp  D, usually a loving husband, suddenly and violently attacked V, his wife. He claimed to be in an autonomous state which could occur from his arteriosclerosis. Devlin J held that non-insane was not available; any internal disorder which affected the faculties of reason/understanding/memory was a disease of the mind. Endorsed in Sullivan  where D suffered an epileptic fit. However, this internal disease must arise from an organic factor - a state of destabilisation brought on by external factors is not legally a disease of the mind e.g. Quick  where D became hypoglycaemic as a result of the insulin he had taken for his diabetes, the courts allowed him non-insane automatism. Contra to Hennessy  where a diabetic failed to take insulin and became hyperglycaemic was denied non-insane. The difference here is that in non-insane automatism, if D raises the defence, the burden of disproof is on the prosecution whereas in the insane defence, D must prove his own automatism. Occasionally, when the reason for D's behaviour is unknown, it is assumed to have been through an internal disorder e.g. Burgess  where D performed a violent act whilst apparently asleep; testimony was given that violent somnamulism was abnormal and must have been caused by some internal disorder. Mirrored the Canadian case of Rabey  where D claimed the shock of his girlfriend rejecting him led him to attack her - the court ruled his reaction was so abnormal that it must have been an internal factor triggered not caused by V's rejection.
V iv(a). The nature and quality of D's act - this means nothing more than the physical aspects of the circumstances and consequences attending D's attack. Many psychotic patients will, within this narrow scope, appreciate the nature and quality of their act. iv(b). Knowledge that D's act is wrong - this is not a test of moral wrongness - D will fail this limb if he a) knows his conduct contravenes the law or b) knows that his conduct transgresses "the ordinary standards adopted by reasonable men". This again allows seriously deranged people to fall outside the insanity defence e.g. Sutcliffe (Yorkshire ripper) D believed it was his divine mission to kill prostitutes - he knew his conduct was contrary to the law however he was in fact schizophrenic to a severe degree but still 'sane' within the laws of insanity. There is some sympathy to the view that this conception is too narrow however the courts have refused the invitation to accept any wider conception of the meaning of 'wrong' which is held always to mean 'unlawful'. INSANE DELUSIONS - R v Bell there is a special section in the M'Naughten Rules to deal with those who are afflicted with a 'partial delusion' but who are not, in the other respects, insane. The responsibility of such a person is to be considered as if the facts with respect to which the delusions exist were real.
CRITICISMS They are in breach of Article 5 of the ECHR (right to liberty) since people with mental illnesses should not be detained unless absolutely necessary for treatment or protection which is not the case under these rules. Addressed in Grant 
There is no statute; only statutory consequences The word 'insanity' is stigmatic and offensive. Interpretations are too narrow for those suffering (e.g. paranoid schizophrenics) and too wide for those not (e.g. sleepwalkers)
Exists in s.2 of the Homicide Act 1957 and s.52 of the Coroners and Justice Act 2009. Where the defence of diminished responsibility is successfully pleaded, it has the effect of reducing a murder conviction to manslaughter To rely on the defence, the defendant must be able to demonstrate the following: i. An abnormality of mental functioning caused by a recognised medical condition. ii. Which provides an explanation for the defendant's acts or omissions in being party to the killing. iii. Which substantially impaired his/her mental ability to either: a) Understand the nature of their conduct or b) Form a rational judgment or c) Exercise self-control i. Abnormality of the mental functioning caused by a recognised mental condition - prior to the CJA 2009, the Homicide Act 1957 referred to "abnormality of the mind". The change of wording was simply to clarify the law and is not expected to make any changes to the applicability of the defence. Thus the case law under the Homicide Act is still relevant. The question of whether the defendant is suffering from an abnormality of the mental functioning is for the jury to decide after hearing medical evidence. The jury are not bound to follow medical opinion e.g. Sutcliffe where the medical opinion was unanimous that the defendant was a paranoid schizophrenic, yet the jury refused to allow him the defence. Examples of what constitute an abnormality of the mind: Byrne  D murdered a young girl staying in a YWCA hostel. He then mutilated her body. He did so as he was suffering from irresistible impulses which he was unable to control. Held: "abnormality of mind" was wide enough to cover the mind's activities in all its aspects, including the ability to exercise will power to control physical acts in accordance with rational judgment. In a case of diminished responsibility the defendant must demonstrate that the characteristic was excessive compared with what reasonable people experience.
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