If your six-year-old is a seasoned little fibber, don't fret - it probably means he or she is unusually bright.

Scientists have found the first clear evidence that children who are good liars have better verbal working memories.

Psychologist Elena Hoicka, a member of the team from the University of Sheffield, said: 'While parents are usually not too proud when their kids lie, they can at least be pleased to discover that when their children are lying well, it means their children are becoming better at thinking and have good memory skills.'

The study involved a quiz in which 114 six and seven-year-old children were tempted to cheat by peaking at an answer written on the back of a card.

First the children were given two easy questions: 'what noise does a dog make?' and 'what colour are bananas?'

They were then asked if they knew the name of the cartoon character Spaceboy. Each child was left alone with an upturned card on which the answer was written, and told not to peek.

The answer, Jim, was written on the back of the card in green ink with a picture of a monkey.

Unknown to the children, they were being observed by a concealed video camera, so the scientists knew who had looked at the back of the card.

Children who got the answer right, and claimed they had not cheated, were tested with 'entrapment questions' based on the written answer and accompanying picture.

The children were asked if they could guess the colour of the writing or what the picture showed. If they covered their tracks by pretending not to know, or deliberately guessing wrongly, they were classified as good liars.

Children who fell for one or both of the entrapment questions, revealing that they knew more than they should, were rated as poor fibbers.

The results, published in the Journal of Experimental Child Psychology, showed that good liars performed better in verbal working memory tests assessing both mental processing and recall.