Sexsomnia, or sleep sex, has only been recognised as a medical condition since the mid 1990s following research done by academics in Canada, and the term "sexsomnia" was first used in 2003.

Sexsomniacs can be men or women and often it is their partners who report their actions as people with the condition are unaware of it.

There has been very little research into sexsomnia, unlike other sleep disorders such as sleep-walking, insomnia and sleep apnoea, where a person stops breathing.

Experts say sexsomnia can become more frequent at times of stress or while a person is under the influence of drink or drugs and can range from mild behaviour to full sex.

According to sleep specialist, Dr Chris Idzikowski, who gave evidence for the prosecution at Adamson’s trial, sexsomnia is most likely to occur when someone is in deep sleep, the stage when the brain’s thinking and awareness is switched off, but not the part of the brain responsible for basic urges.

Sexsomia has been featured in television drama programmes such as House, Law and Order and Desperate Housewives.

In 2012 Hollyoaks actor Simon Morris was jailed for eight years after being found guilty of raping a 15-year-old girl at a house party.

He had claimed he suffered from sexsomnia but the jury did not believe him.

In recent years an increasing number of men accused of rape or sexual assault have used sexsomnia as a defence in court cases.

The explanation has been accepted by juries in at least 12 such cases and the defendants have been acquitted.