Automatism arises where the defendant’s act was involuntary – in Lord Denning’s words, “an act done by the muscles without any control by the mind” (Bratty v Attorney-General for Northern Ireland [1963] AC 386). Because criminal liability normally requires a voluntary act, a defendant acting in a state of automatism has not committed the offence. Which kind of automatism it is, however, makes a great deal of difference to the outcome.
What automatism is not
The loss of control must be total. Reduced or impaired awareness is not enough: a driver who was “driving without awareness” but retained some control was not acting as an automaton (Attorney-General’s Reference (No 2 of 1992) [1994] QB 91). Nor is automatism the same as an irresistible impulse, difficulty controlling one’s temper, an unintended consequence, or a lack of memory for the act afterwards.
Insane and non-insane automatism
The law divides automatism by its cause.
Non-insane automatism has an external cause – a blow to the head, the effect of a drug taken on medical advice, or hypoglycaemia brought on by insulin (R v Quick [1973] QB 910). If it succeeds, the defendant is simply acquitted.
Insane automatism has an internal cause, and is governed by the M’Naghten Rules. Epilepsy (R v Sullivan [1984] AC 156), hyperglycaemia from untreated diabetes (R v Hennessy [1989] 1 WLR 287) and sleepwalking (R v Burgess [1991] 2 QB 92) have all been treated as internal causes. The outcome is the special verdict of not guilty by reason of insanity, with the disposals that follow.
The distinction can seem arbitrary: a diabetic defendant who took too much insulin may be acquitted outright, while one who took too little falls within the insanity rules. It is nonetheless the law, and it makes the precise medical cause of the episode central to the case.
Self-induced automatism
Voluntary intoxication with alcohol or drugs does not found a defence of automatism (R v Lipman [1970] 1 QB 152). Where the automatism was self-induced in some other way – for example, by failing to eat after taking insulin – the defence may still be available unless the defendant was reckless about the risk (R v Bailey [1983] 1 WLR 760).
Proof
For non-insane automatism the defence must lay a proper foundation for the claim, which in practice almost always means medical evidence; the prosecution must then disprove it beyond reasonable doubt. For insane automatism the burden lies on the defence, on the balance of probabilities, as with any insanity defence.
Sleepwalking
Sleepwalking is the classic modern example, and since Burgess it has been treated as insane automatism. Clinically, sleepwalking episodes typically arise from deep sleep in the first third of the night; the person may appear purposeful but has a blank expression, is difficult to wake and unresponsive to others, and usually has no memory of the episode afterwards. Any confusion on waking is brief. Whether an episode fits that pattern – and whether alcohol, sleep deprivation or stress played a part – is at the heart of the expert evidence.
What the psychiatric report addresses
An automatism report addresses whether there is a recognised condition capable of causing a complete loss of voluntary control – such as epilepsy, a parasomnia, hypo- or hyperglycaemia, a dissociative state or head injury – whether the evidence about the episode fits that condition, whether the cause was internal or external, and the role of any intoxication. It will often recommend specialist investigations, such as neurology or sleep studies, where they would assist the court.