Automatism: Condition with a long legal history

automatism - acting involuntarily or subconsciously - has been recognised by Scots law for generations.

One of the most celebrated cases is from 1878, involving Simon Fraser, who was charged with murdering his 18-month-old son by fracturing his skull. A special plea was entered that Fraser had been asleep. He had had a nightmare in which he was being attacked by an animal, and the court was told he had a history of sleepwalking, sometimes with violent behaviour.

The judge said there was not the slightest doubt Fraser had been totally unaware of what he was doing. Fraser was released, having undertaken to sleep alone in future.

In a more recent case in Wales, a husband who strangled his wife while having a nightmare about intruders was freed after the prosecution accepted he was not in control of his actions.

Brian Thomas, 59, of Neath, had been prone to sleep disorders and he and Christine, his wife, slept in separate bedrooms. However, they shared a bed when they went on holiday in their campervan.

In July 2008, they took the van to a seaside village, but were disturbed by "boy racers" performing wheelspins late at night. They settled down but, later, Thomas made a 999 call to the police, saying he had strangled his wife in his sleep.

He said: "What have I done? I've been trying to wake her. I was fighting with those boys but it was Christine. I must have been dreaming."