Automatism
Automatism applies to the situation where the defendant is not legally insane but because of some external factor he is unable to control what he is doing, or as Lord Denning stated in Bratty v Attorney-General for N. Ireland [1963] AC 386, where something was done by the defendant's muscles without the control of his mind, such as a spasm, a reflex action or a convulsion; or an act done by a person who is not conscious of what he is doing, such as an act done whilst suffering from concussion or whilst sleep-walking (although sleepwalking is now regarded as legal insanity).
It can then be argued that there is a lack of actus reus, as the act is not voluntary, or that there is a lack of mens rea because the defendant is not conscious of what he is doing. The defendant must fulfil two conditions:
A) TOTAL LOSS OF VOLUNTARY CONTROL
The defence is not available where the defendant's mind is
functioning, albeit imperfectly. See:
Attorney-General's Reference (No 2 of 1992) [1993] 3 WLR 982.
B) EXTERNAL FACTORS
This inability to control one's acts must result from the operation
of some external factor upon the working of the brain, rather than
an inherent mental defect. See:
R v Quick [1973] QB 910. The external factor could be a
traumatic event including severe shock, although it must be
something which results in more than general stress and anxiety. A
good example is rape which lead to Post Traumatic Stress Disorder
in: R v T [1990] Crim LR 256)
C) SELF-INDUCED AUTOMATISM
A defendant may be prevented from raising the defence of automatism,
where there is evidence to show that he was in some way at fault in
bringing about the state of automatism. The principal authority on
this point is the Court of Appeal decision in:
R v Bailey [1983] 1 WLR 760. If the defendant is charged
with a specific intent crime, he will have a defence if mens rea was
not formed. If it is a basic intent crime, the defendant will have
no defence if he was reckless.
D) EFFECT
Automatism operates as a complete defence in that if the defendant
succeeds in establishing it, he will be acquitted, and the court
ceases to have any jurisdiction over him. Where a defence of
automatism is raised, the courts will have to consider whether the
defendant should in fact be classed as criminally insane.