Scientists may have the answer to why the opposite sex seems more enticing after a few pegs - they found that alcohol clouded women's judgement.

Researchers at London's Roehampton University asked more than 100 men and women to rate pairs of faces. Some did the tests while drinking a strong vodka and tonic. Others were given a similar-tasting non-alcoholic drink or orange squash.

One of the tests involved looking at faces and stating whether they thought each one was symmetrical or non-symmetrical. Symmetry is known to be tied to attraction, with a face in which one half mirrors the other seen as a sign of good genes and good health, the journal Addiction reports.

The men and women given the vodka and tonic found it more difficult to work out if a face was symmetrical than those on soft drinks, according to the Daily Mail.

Roehampton researcher Lewis Halsey said: "People that had drink tended to be less good at noticing if a face was asymmetrical, they often saw it as being symmetrical when it was asymmetrical."

Halsey said: "What we have shown is that people's ability to detect symmetry is part of the explanation for the beer goggle effect. The consequences could be considerable.

"A lot of people say they met their partner when they were drunk. Are their marriages shorter or longer lasting? Does it change the nature of the relationship?"

A Bristol University study found people do appear more attractive to both sexes after they've had a drink - and it takes as little as a pint and a half of beer. In some cases, the mere anticipation of alcohol may be enough to alter judgement.