The interview took all day. I had sat with a gang member in a South London youth centre for hours. We covered his grim story in full: his upbringing (father had left, mother struggled to support him and his brother), expulsion from school, his first involvement (“shotting” or dealing, wraps of cocaine), when he was stabbed, the violence in his area, his hopes and fears.

As I got up to leave, he looked at me for what felt like the first time. “You think you get it: you don't. You never even asked about my brother.” I waited. “He's a trainee solicitor. What do you make of that?”

Gangs are an epidemic, too widespread to trace their roots to any one social factor. Take parenting. Many gang members come from broken homes, or a background of drug abuse and domestic violence. Fix the family and you fix the child, runs the mantra. But what of the gang member with two loving but busy parents, one of whom was a local councillor?

During two years of research for my book on Britain's gangs, One Blood, I saw how they instil fear in everyone, old or young. One boy refused to join a gang in East London: he was beaten up, his sister raped. How can parents be blamed?

There is no constant about gangs that suggests a single answer. The Government supports tough policing. Of course, those who commit stabbings and shootings must be caught and punished. But prison is not enough to deter those inspired by successful criminals, while rehabilitation and jobs for former offenders are severely limited.

One youth worker told me: “What am I supposed to tell a gang member? Give up the lifestyle and the hundreds you're making every week, and live like a tramp? Because they know I'm lying if I say I can turn their lives around any time soon.”

I met gang members who had gone straight after a lengthy stint in prison but they are the exception, not the rule. Time and again they said that rehabilitation is a myth.

Such is the extent of the problem that one could pick almost any government scheme and argue that it will have only limited impact. One recent initiative uses hard-hitting images of the wounds that knives cause. It may deter some youths who carry a blade for protection. But those who enjoy the power afforded by a knife are not bothered by state advertising. I met several youths who are well aware of the damage that a knife can do, and do not care.

To anyone who works with those at risk of getting involved in gangs, none of this is new. But what is surprising is just how old they are. In 1927 Frederic Thrasher, a sociologist at the University of Chicago, undertook a study of the city's 1,313 gangs. The resulting book, The Gang, is a classic. In analytical terms it is endearingly amateur - he tended away from the heavily researched graphs and had no hypothesis he wished to test. But this does not make his work naive. Above all, he understands how important it is to see gangs in geographical terms. He dubs these places “interstitial” areas, “isolated from the wider culture of the larger community by the processes of competition and conflict which have resulted in the selection of their population”.

For Thrasher, these areas existed between mainstream societies: between Chicago's central business district, the Loop and its better neighbourhoods. It is little different in Britain today, where rich and poor have moved apart physically as well as economically, and where the latter are congregated in enclaves between the former. These are recognisable in London in places such as Brixton, Hackney or Peckham, where a high number of people have moved in and out over the years.

The key point about these places, Thrasher says, is that they are disorganised. People mill around without direction, diverted from a stable life of education or employment. A key point about such areas is that crime is always there - but the idea of the gang gives it cohesion. Being a gangster is a template for living in gangland.

Here is Thrasher writing a chapter entitled “Attacking the Problem”: “Such underlying conditions as inadequate family life; poverty; deteriorating neighbourhoods; and ineffective... education and recreation must be considered together as a complex situation which forms the matrix of gang development.” I agree that gang-involved youths must not be treated as if they are in a “social vacuum but... as a member of the family, the neighbourhood, the school...”

When he writes that “too often [the gangster] has been dealt with as if he were a purely biological, predetermined mechanism”, he could be talking about our policies today. The Government's modest Tackling Gangs programme has shown that local voluntary and statutory agencies must work together. Voluntary workers tend to be local and have the credibility to engage with people, not problems.

In her speech to the Labour conference last year Jacqui Smith, the Home Secretary, spoke of her faith in “21st-century crime-fighting techniques”. Thrasher's analysis may be more than 80 years old, but it might be of more use.

John Heale is the pseudonym of an investigative journalist. One Blood: Inside Britain's New Street Gangs is published by Simon & Schuster

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