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 was, however, makes all the difference to the outcome.
A total loss of control
The loss of voluntary control must be total. Impaired or reduced awareness is not enough. A driver who had become hypoglycaemic but was still able to steer and react to some extent was not an automaton (Broome v Perkins (1987) 85 Cr App R 321), and nor was a lorry driver said to have been “driving without awareness” after hours on a motorway (Attorney-General’s Reference (No 2 of 1992) [1994] QB 91). Automatism is also distinct from an irresistible impulse, a failure to control one’s temper, an unintended consequence, and an inability to remember 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 orders that follow it.
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 of becoming aggressive, unpredictable or uncontrolled (R v Bailey [1983] 1 WLR 760).
Proof
For non-insane automatism, the defence must lay a proper foundation for the claim before it can go to the jury, which in practice almost always means medical evidence; the defendant’s own account of a “blackout” is rarely enough (Bratty). 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, and the statutory requirement for two medical practitioners applies.
The conditions involved
Epilepsy. Complex partial seizures and post-ictal confusion can produce apparently purposeful behaviour without awareness. Because the cause is internal, a successful defence leads to the special verdict.
Diabetes. Hypoglycaemia from insulin is external; hyperglycaemia from the disease itself is internal. The timing of meals, insulin and blood glucose readings often decides which applies.
Sleep disorders. Sleepwalking and related parasomnias 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; any confusion on waking is brief. Whether an episode fits that pattern – and the part played by alcohol, sleep deprivation or stress – is at the heart of the evidence.
Dissociative states. Severe dissociation, for example following trauma, may in principle found the defence, but the courts scrutinise such claims closely, and whether the cause is classed as internal or external depends on the facts.
Head injury and concussion. A blow to the head is the classic external cause, but the evidence must show a total loss of control at the time of the act, not merely later amnesia.
What the psychiatric report addresses
An automatism report addresses whether there is a recognised condition capable of causing a complete loss of voluntary control; whether the evidence about the episode – its onset, duration, the defendant’s behaviour and their recovery – fits that condition; whether the cause was internal or external; and the role of any intoxication. It will often recommend specialist investigation, such as neurology or sleep studies, where that would assist the court, and it identifies the limits of what psychiatry can say about an episode no one recorded.