What is automatism?
Generally, at common law, a voluntary act is required to establish the actus reus of a crime. The defendant should also be conscious of their acts so that mens rea can be established. A defendant may, however, plead automatism, which if successful will result in an acquittal. Automatism as a defence seeks to show that a crime was the result of an involuntary act caused by an external factor.
Automatism distinguished from insanity
If automatism is the result of a disease of the mind then this is properly insanity and a trial judge is entitled to withdraw the defence of automatism from the jury following Bratty v Attorney-General for Northern Ireland . On the other hand, a diabetic who overdoses on insulin causing them to suffer hypoglycaemia will not be suffering a disease of the mind and may be able to plead automatism. (Compare this to R v Hennessy , where a diabetic suffering from hyperglycaemia was judged to have a disease of the mind and consequently was criminally insane. For a better understanding, hypoglycaemia is a state induced by a lower than normal level of blood glucose. Conversely, hyperglycaemia is when there is an excess of glucose in the blood plasma.) The jury will have to decide whether the defence is made out and that the defendant was acting involuntarily due to an external factor (see R v Quick ).
Drunkenness and drugs
Automatism induced by alcohol or drugs is, as a matter of public policy, incapable of being a legal defence. This is generally because there is a high number of crimes committed under the influence of alcohol, and increasingly nowadays drugs, which would otherwise go unpunished. In R v Lipman  the defendant was convicted of the manslaughter of a girl who he had killed whilst under the influence of LSD. In confirming the conviction, the Court of Appeal held that mental states induced by drink or drugs are no defence to a charge of manslaughter, which, in any event, is an offence that does not require specific intent.
For more information on:
- Drunkenness or drugs not self-induced