IF only everyone was as easy to spot telling a fib as Pinocchio - the Disney children's favourite whose nose grew when he lied.

Scientists already know that when people are untruthful their heart rate increases and they sweat more.

Now one Southampton psychologist has made another major breakthrough in detecting those who don't always think honesty is the best policy.

Dr Aiden Gregg, of the city's university, has found that it takes longer to tell a lie than to tell the truth.

He carried out three studies using between 30 and 50 volunteers to repeatedly confirm or deny jumbled-up statements by pressing one of two keys on a computer as quickly as possible.

The statements were a mixture of questions about the world at large or personal details about the participants themselves.

Dr Gregg instructed one group to classify statements about themselves as false and statements about the world honestly.

He found this group took between half a second and a second longer to complete the task than truth-tellers, who were allowed to respond honestly to both sets of statements.

From his experiment Dr Gregg, a research fellow at the university's centre for research into self and identity, concluded that it takes longer to tell a lie than to tell the truth.

Dr Gregg said: "The aim of the experiment was to come up with a lie detector that could be used on a computer which is easy to use.

"It's all about doing two incompatible things at once. It's very difficult and a bit like trying to rotate one arm clockwise and one leg anti-clockwise."

Dr Gregg added that there was still a long way to go in producing the final lie detector.

He said: "Young and old people would differ in their reaction times so some sort of scoring system would have to be established to take that into account."

Dr Gregg added that the lie detector, which was more than 85 per cent effective in the test, could be used in police interviews.

However, he warned against using it as an absolute test of guilt because it would not be 100 per cent accurate.

In the experiment there was no marked difference between the ability of women and men to hide the fact that they were telling porkies.

"I don't think there is a gender difference. Age and intelligence would be more important factors," he said.