A study of 400 young men from south London shows that a football hooligan is more likely to be below average height and tattooed.

The study, started in the late Sixties by the department of psychological criminology at Cambridge, gives football clubs and police a new profile of offenders before the season opens this Saturday. It has monitored the group's school, employment and criminal careers since the young men were eight-year-olds. They are now in their early thirties.

Professor David Farrington and his team have come up with six profile factors to help teachers, police and social workers to identify those at risk of becoming persistent offenders.

The Professor says that being short and/or tattooed are markers of criminal involvement - he likens tattoos to a bar code that helps to detect lawbreakers.

The survey shows that being below average height turned out to be the best predictor of being a football hooligan - apparently because shortness may give people a 'Napoleon complex.

Almost half the offenders wore tattoos, according to the survey, and half were heavy drinkers and smokers at the age of 18. At this age two-thirds had used drugs and by the age of 32 many had moved to harder drugs - cocaine and heroin.

They had high levels of sexual promiscuity but rarely used contraceptives and had a his-tory of broken relationships.

Nine out of 10 had left school at 15 and had taken no examinations.

The six factors showing those at risk were: coming from a low income family; having a parent with a criminal conviction by the time the child was 10; harsh and erratic discipline during childhood; being troublesome at school at the age of eight; being 'daring at an early age; a low IQ and little educational attainment.

Between the ages of 10 and 18, three-quarters of the boys had not been convicted of any offence. However, 66 of the 400 surveyed had committed one or two offences and 45 had convictions for three or more.

The survey found almost half the persistent offenders came from families where a parent had been convicted of a crime by the time they were 10. Two-thirds had friends who were delinquents.

The survey, says Professor Farrington, not only provides a profile of persistent offenders but highlights factors that may help to identify potential offenders at a young age.