The number of young offenders who blame alcohol for their crimes has almost doubled in the last 30 years, according to the most comprehensive study into drinking and violence in Scotland.

The study by Bill McKinlay, governor of Barlinnie prison, and academics at Glasgow Caledonian University reveals a startling insight into offending and alcohol misuse over time.

Contrary to public perception, very few of the young offenders going into prison blamed drugs for their crimes but they increasingly claimed the problem is due to drinking. And offenders were far more likely to carry weapons and be more violent when drunk.

In 1979 some 29.5% of the young men blamed their offence on alcohol compared to 40% in 1996 and 56.8% in 2007.

More than two in five - some 43% - of the inmates interviewed in 2007 revealed they had drank Buckfast immediately prior to their offence. The number blaming just drugs dropped from 21% in 1996 to 9% in 2007.

"Originally when I saw the research I found it hard to believe," said Dr Alasdair Forsyth, senior researcher at the Glasgow Centre for the study of Violence. "It's not common to get findings as spectacular as this but these are the results.

"The study indicates that drink per se does not cause people to be violent but it encourages them to go much further than they would have done otherwise. They said that if they were sober they would not have got caught - not that they would have been deterred from offending. If they do blame drugs, they blame Valium not heroin.

"In 1996 when there was more of a drug-using population - they tended to be less involved in serious violence.

"When we were fixated by drugs in the 1980s, alcohol was almost ignored as a problem and people started drinking more.

"The fact is that alcohol never went away and is now more of a problem than before." The research is based on questionnaires and interviews with 96 young offenders aged between 16 and 21, in 1979, 152 in 1996 and some 172 last year. The study found that the proportion of young offenders involved in serious violence including murder and attempted murder rose from 22% in 1979 to 53% in 2007.

In 1996 - the year that more offenders blamed drugs rather than alcohol - the number dipped to 10%.

The preliminary results of the study will be presented at the Holyrood Alcohol and Violence conference in Edinburgh today.

Further results investigating why young offenders drink and become involved in violence will be presented later in the year.

Mr McKinlay, the then assistant governor of the young offenders' institute at Glenochil, began the research himself in 1979.

It was later continued by David Shewan, a leading researcher at Glasgow Caledonian who died last year.

"I was genuinely surprised to see the parallel increases in alcohol and associated negative behaviour, especially in the area of violence," he said.

"For a number of years we've been concentrating on illicit drugs whereas, in fact, the research shows that