People who believe they have been kidnapped by aliens were probably just dreaming, a leading researcher claims.

However real the experience may have seemed –  involving space travel or sexual encounters with extraterrestrials – it is most likely to have been caused by borderline sleep, Dr Susan Blackmore, a researcher in the paranormal, has found.

Dr Blackmore, of Bristol, United Kingdom, identified "sleep paralysis" as the likely culprit for most alien kidnap experiences.

Although only a few people report alien encounters, she has found sleep paralysis is a common, if unnerving, experience shared by up to three out of 10 people.

The dreamer hears strange noises, sees flashing lights and senses shaking or juddering.

Some feel they have been turned in their beds, while others report sexual encounters.