R v Quick [1973] QB 910

Quick was a nurse with diabetes who assaulted a patient. Before the incident he had taken insulin, consumed little food and drunk alcohol. He claimed to remember nothing of the assault and relied on evidence that he had suffered hypoglycaemia, an abnormally low blood-sugar level caused by the insulin. The trial judge ruled that any defence based on his diabetic condition had to be insanity rather than automatism. Quick then changed his plea to guilty and appealed. The medical evidence distinguished hypoglycaemia caused by injected insulin from hyperglycaemia caused by the underlying diabetes. The Court of Appeal considered whether the alleged malfunction arose from an external factor and whether the jury should have been allowed to consider automatism.

Was Quick's alleged loss of control caused by an external factor capable of supporting sane automatism, or by an internal disease of the mind requiring the insanity rules?

The Court of Appeal allowed the appeal and quashed the conviction. If Quick's mental state resulted from hypoglycaemia caused by insulin, the malfunction was attributable to an external factor and could in principle support automatism. The judge had therefore been wrong to rule that insanity was the only possible defence. The Court contrasted this with a malfunction produced by diabetes itself, such as hyperglycaemia, which later authority treats as an internal disease of the mind. The availability of automatism still depended on evidence of a total loss of voluntary control. It could also be defeated where the condition was self-induced and the defendant had been reckless in failing to eat or manage a known risk, particularly for a basic-intent offence.

A total loss of voluntary control caused by an external factor may amount to sane automatism. Hypoglycaemia produced by insulin is external for this purpose, whereas a malfunction caused by the underlying disease may fall within insanity. Self-induced automatism may be unavailable where the defendant culpably created a foreseeable risk of offending.

The case is the principal authority for the internal and external cause distinction between insanity and automatism. It is not enough that a defendant has diabetes; the court must identify what caused the episode. R v Hennessy treats hyperglycaemia arising from diabetes as insanity, while R v Sullivan confirms that a temporary internal malfunction can be a disease of the mind. R v Bailey addresses self-induced hypoglycaemia and recklessness. The distinction has major procedural consequences because sane automatism may lead to a complete acquittal, whereas insanity produces a special verdict and statutory disposals.