It is theholy grailof politicians everywhere - how to win and keep the trust of voters.

Now researchers at the University of St Andrew's in Scotland say they may have the answer.

They believe politicians could learn a lot from recent advances in science.

A growing number of studies have shown that people do judge a book by its cover.

Researchers say most of us make instant judgements about a person on the basis of how they look.

They sayfacial featurescan determine whether we like or trust someone. It may even influence how we vote.

"Over the years, we have found that facial features affect the way many of us perceive others," says Elisabeth Cornwell, a psychology researcher at the university's Perception Laboratory.

Studies suggest that people are less likely to trust those with particularly masculine features, such as a square jaw, small eyes or big nose.

"They are perceived as dominant and less trustworthy," says Ms Cornwell.

"It doesn't mean that men who look more masculine are less trustworthy - it's just our first impressions."

Those with less masculine features - larger eyes, a smaller nose and thinner lips - are deemed to be more trustworthy.

"We are very good at processing these features quickly," says Ms Cornwell.

The researchers are putting their science to the test at the Royal Society's annual summer exhibition in London.

They have subtly manipulated the faces of Prime Minister Tony Blair, Conservative leader Michael Howard and Liberal Democrat leader Charles Kennedyaccentuatingtheir dominant and trustworthy features respectively.

"We have used a computer programme to change the shape of their face and features.

"We hope it will help people to understand our work."

So should we expect to see Tony Blair, Michael Howard and Charles Kennedy at the exhibition getting tips?

"I don't think it's something they will want to try," says Ms Cornwell.

"It's not really possible with television. We all know what they look like. I think they would be naive to try it."

(Agencies)