As many as a fifth of 18-34 year old black men in Hackney could be part of a gang according to researchers.

The figures emerged in a study which concluded gang members suffer unprecedented levels of psychiatric illness, placing a heavy burden on mental health services.

Researchers at Queen Mary, University of London, surveyed 4,664 men aged 18 to 34 in Britain, with the sample weighted to combine significant numbers from areas with high gang membership - including 700 from Hackney.

Of the total sample 2.1 per cent of men said they belonged to a gang - but in Hackney the figures were much higher at 8.6 per cent. If membership of a gang is narrowed down to black men in Hackney the figure shoots up to 20 per cent.

Violent ruminative thinking, violent victimisation and fear of further victimisation were significantly higher in gang members and believed to account for high levels of psychosis and anxiety disorder.

Professor Jeremy Coid, director of forensic psychiatry research unit at Queen Mary, and lead author of the paper said: “One of the most interesting things is that you actually have a real changing social demography in Hackney. So if we look at white men in Hackney the figures are fractionally higher than the rest of the country for gang membership, but it’s extremely raised among black men.

“There are a lot of middle class men in Hackney now with house prices going up, there’s a demographic change and almost two completely different segments of the population with different social circumstances.

He continued: “Another area we studied was Glasgow East in Scotland which is even more socio-economically deprived than Hackney, men there say they get into gang fights and the level of violence is extremely high, but it’s not so unequal.

“There’s been an outward movement from Hackney of white people of lower social class, maybe if we can get some more research money we can extend our survey south of the river to Lambeth.

“You can’t be sure it represents Hackney, only as much as you can be sure of anything in terms of survey work, you are in the hands of your surveying company.”

No previous research has investigated whether gang violence is related to psychiatric illness other than substance misuse, or if it places a burden on mental health services.

Of the 108 gang members surveyed, 85.8 per cent had an antisocial personality disorder, two-thirds were alcohol dependent, 25.1 per cent screened positive for psychosis and more than half were drug dependent.

Professor Coid added: “It is probable that, among gang members, high levels of anxiety disorder and psychosis were explained by post-traumatic stress disorder, the most frequent psychiatric outcome of exposure to violence.

“However this could only partly explain the high prevalence of psychosis, which warrants further investigation.

“A potential limitation of the study is that survey participants were aged 18 to 34 and the average age for gang membership is 15.

“So gang members in this study should be considered ‘core’ gang members who have not stopped in early adulthood.”