He grew up on the Red Lion Estate in East Finchley - dubbed "Hungry Hill" by locals - the son of Irish immigrants. His father was a gambler and alcoholic who abandoned his mother to look after John and his brother Mick. The pressure of bringing up two boys in what remained a strange and daunting city hit their mother hard. She succumbed to bouts of mental illness, whereupon the boys would be packed off to Catholic foster homes.

Although he was a tearaway and shoplifter, JJ insists he was a poor thief with a knack for getting caught. His criminal days ended in his teens when - after being nicked for stealing a case of Scotch from a local football club - he was told by a policeman (or "cozzer", as one of his characters would put it): "You're not very good at this thieving lark, are you?"The years passed, and so did practically every type of job imaginable With one exception Connolly is adamant that he has never been a cocaine dealer "Don't worry," he says. "You won't get anyone jumping out of the woodwork saying, 'Oh yeah, I know JJ Connolly - he used to sell drugs.' I'd be a very bad drug dealer If you're a drug dealer, you've got to scare people I'm the least threatening person I can think of. Anyone who thinks I'm a gangster has obviously never met a real one."YetLayer Cake is a novel that oozes authenticity. The passages describing the nuts and bolts of Class-A distribution, for example, have a worrying authority. Connolly insists this is simply because people tell him things "Rehab isn't fun," he says "You turn yourself inside out But you meet people who have really lived There aren't many shallow people in rehab. Everyone's got stories to tell." Certain Layer Cake "consultants" will have to remain nameless, however.

Connolly may not be a criminal himself, but he will admit to knowing people who have "ducked and dived a bit, been up to all sorts". They helped out with the finer details.Even though people assume he spends his days now hanging out with Madonna and Claudia Schiffer (Matthew Vaughn's wife), Connolly insists his close friends are the same gang he's hung around with for years. One is a shirt-maker, another works in PR, there's a portrait painter, a florist.. in short, not exactly London's criminal underbelly. He lives in King's Cross with his commercial-producer girlfriend of three years, Rebecca, and is busy with his next book."It's a sort of Lord of the Rings of the criminal underground," he says. "A quest." He treats writing like a job, setting himself a target of 1,000 words a day. And he's bought himself a laptop.The new edition of 'Layer Cake' (Duckworth, £7.99) is published on 9 September The film is released on 1 October. Part of the grim power of murder, real or fictional, is the ability to shine a harsh light on its context.