A "Sting" type experiment using psychology graduates to harass volunteers has shown that alcohol has no direct influence on aggression.

Niall Coggins, senior lecturer in Strathclyde University's department of pharmaceutical sciences, investigated 130 volunteers who believed they were taking part in a study of alcohol and coordination.

They had drunk orange juice containing either no alcohol, the equivalent of four measures of spirits, or the equivalent of eight measures, and were then asked to fill in extensive questionnaires and attempt reaction time tasks and games on a computer.

"I created a fog round the key event," Mr Coggans said. A person would come into the room and brusquely interrupt, demanding to use the computer. Mr Coggans would react mildly or equally curtly. If he had reacted curtly, once the person had left, he would make derogatory comments about them to the volunteer.

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Then he too would leave, and the person, in fact a psychology graduate involved in the experiment, would burst in and insist on the volunteer giving up the computer, in some instances going as far as to switch it off, while hidden observers checked the volunteers' reaction.

This ranged from the placatory to squaring up to the interloper and telling them to "F-off". But the key predictor of the volunteers' aggression was not the amount of alcohol they had taken, nor even their personality, but Mr Coggans's initial reaction to the interruption.

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"There was no relation between alcohol and aggression. The thing that made the difference was whether or not I had included this aggression priming element - you could say there was a degree of implicit permission to behave in a certain way."

Mr Coggins concludes that so-called alcohol-related violence has less to do with alcohol as such than with the social context in which people drink. In some rough bars, for example, a degree of swearing might be acceptable, but there would be a clear code of conduct making fighting unacceptable.

"Intoxicated people are aggressive, not so much because they have been drinking, but because of social cues from people around them. There's nothing about the pharmacology of alcohol which makes you swing a punch."