Four years ago, when the actor Lennie James first appeared on stage in Fallout at The Royal Court Theatre in London, its subject matter - the stabbing of a black youth on a South London housing estate - was all too topical.

Written by the award-winning dramatist Roy Williams in the aftermath of the Stephen Lawrence and Damilola Taylor cases, it was a powerful tale from the front line of what was fast becoming a street war. Then, as now, guns and knives were the weapons of choice, and teenage boys were the casualties.

“At that time we were asking the questions, 'When will this war stop? And what can we do to end it?'” says James, who is at the offices of Channel 4 to talk about reprising his role for a TV version of Fallout.

“But four years down the line what scares and disappoints me is that those questions are even more relevant now. An insane amount of young people have lost their lives since we first staged Fallout.”

Indeed, since 2003 more than 350 teenagers have been shot or stabbed to death by other teenagers or young adults. This year, so far, 16 have died in London alone. “And you know that's a lot of young people who are not going to live the lives they were going to live. And that brings shame on all our heads.”

It's timely, then, for Channel 4 to launch a series of programmes that will address the issue of gun and knife crime on the streets of Britain. It's not surprising, either, that Fallout, which has now been updated by Williams, should be billed as its traumatic highlight.

“Fallout's an unapologetically hard- hitting drama,” says James. “There's not too many laughs in it, but, importantly, it takes a hard look not just at the teenagers involved but also at the police and at society at large, because all of us living our comfortable lives bear some responsibility. And if we want to fix this situation we can't just put our heads in the sand.

“The bottom line,” he adds, “is that I don't want to be sitting here again in four years time having the same conversation with you. I want to be able to say, 'Can you believe how it was back then?' What I want most is for this war to stop.”

The last line is borrowed from James's character, Joe Stephens, a police officer returning to the estate where he grew up to investigate the killing of 16-year-old Kwame (played by Lanre Malaolu). A promising student, he falls foul of a local gang who stab him to death, apparently, for nothing more than his trainers.

“Although, of course, what the killing is actually about is what it's always about,” says James. “It's about young boys growing up in a culture where violence equals respect. It's all there in Fallout: saving face with your boyz, blaming everyone and everything for who you are and what you've done. And what we're talking about here is second-generation violence. These kids have grown up watching adults espousing the same crazy ideas about manhood.

“That's why, personally, I'm willing to stand up and do anything to get an alternative message across. To get these kids to think, 'I don't buy into this mentality. I don't accept this as a viable means of growing up.'”

Clearly Fallout is an intensely personal project for James. As a black actor raised in the socially deprived area of Tooting in South London, he feels a sense of responsibility to the community from which he came. “And the thing I'm most proud of is when people from my community come up and say: 'We like what you are doing.'”

Although currently living in Los Angeles, he negotiated a break from Jericho, the US series on which he was a regular, to return to Britain to film the drama. “But then I'd have been upset if they hadn't asked me to play Joe again,” he laughs. “I'd have had to hurt someone!”

Not that violence is in his nature. The 42-year-old actor has an intense, lean, powerful physical presence that would make him scary in a fight, but when he's vexed it's words that he falls back on. He's written articles and plays including the RTS-award-winning Storm Damage about the subjects of race and violence, and the need for role models. “They're all subjects I feel strongly about,” he says.

Born to Trinidadian parents, James never knew his own father. But his mother Phyllis Mary James was his first role model. She died from pneumonia when Lennie was about to turn 11. “But long before my brother and I lost her she was always making sure that her boys were never going down the route of violence and crime. And after her death there were other mentors in my life who kept me safe and on the straight and narrow, especially my foster mother, an incredible, kind, loving woman, who took me under her wing.

“These days black kids idolise the ones that got away: the singers, the footballers, the boxers. And that's great. But the real heroes are ordinary people like my foster mum who are saving people's lives every day.

“Isn't it time we sat down with young men and said: 'You see the guy over there who's working to provide for his family and keeping them fed and safe? He's the man that you should aspire to be. You don't need to be any more special than that.'”

Lennie himself has raised three daughters: Romy, 17 and twins, Celine and Georgia, 13, with his long-term partner, Gisele Glasman. Still, not surprisingly perhaps, he's also godfather to five boys. “And, you know, I take that role incredibly seriously because I see it as a privilege to be a mentor in the way that people were to me.”

He takes the parts that he plays seriously, too. These have included British TV and film roles in Undercover Heart, The State Within and 24 Hour Party People. But when he was fresh out of the Guildhall School of Music and Drama, casting directors showed a worrying determination to cast him as pimps or gangsters.

“I refused those roles because I didn't want to go home to my brother or my foster mum and have them say: 'What are you doing? How does that represent the people of your community?' So I ended up playing a lot of police officers instead. Now who'd have thought that?” he smiles.

The irony is that Lennie's experiences of the police while growing up in London were diabolical. “The first person who used the 'N' word to me was a policeman,” he says “I was 11 years old and riding my bike on the pavement.

“Later, as a teenager and young man, I lost count of the number of times I was hit and thrown to the floor by a policeman before I was asked what I was doing or where I was going. As black people we were sport as far as the police were concerned.”

That plans are afoot to bring back stop-and-search practices appals him. “Somewhere in there is the notion that knife crime is a black problem. But go to Glasgow - the knife capital of Britain - and it's predominantly young white men who are the perpetrators. And by saying it's a problem with black folk you ignore the reality that it's poor folk.”

It's disappointing too, he says, that the police are still more hooked on punishment than on prevention. But if you're a kid out there who's thinking that this or any of the other umpteen things that you could feel angry about excuses the knife in your belt or the gun in your pocket then you are wrong.

“That is the real message of Fallout.”

Fallout, Thur, Channel 4, 10pm

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