One Love Community Association says the sign perched high on the wall of a run-down unprepossessing building in Plaistow, east London. Inside a portable office in the grounds, Ray Lewis, tiny and dapper in shirt, tie and polished black shoes, offers me a drink. When I decline, he grins: “Good, I don’t do tea, coffee . . . or small talk.”

It’s a surprising place to find the Tories’ favourite black activist, who has just become Boris Johnson’s deputy mayor in charge of tackling youth crime in London. It will be a tough brief but if anyone has the tools and ideas to stop teenagers armed with guns and knives terrorising the rest of us, it is Lewis.

From these cramped rooms this former prison governor and ordained minister launched the work that has convinced successive Tory leaders — from Iain Duncan Smith to David Cameron — that he has “tough love” solutions to one of the most chilling social problems of our times.

Few can have failed to notice the pandemic of feral youth crime sweeping the country. Gang warfare has left youngsters stabbed or shot or kicked to death everywhere from Manchester to Southampton. Everyone knows about 11-year-old Rhys Jones, gunned down while coming home from football practice in Liverpool — but what about the A-level student Kodjo Yenga, who died one tea-time on a west London pavement after being caught by a mob; or the goth girl Sophie Lancaster, stamped to death in Lancashire when she tried to save her boyfriend from a gang attack?

Hardly a day seems to go by without a horrifying atrocity that leaves parents grieving and the rest of us wondering what on earth is going on.

Lewis understands the descent into such violence better than most: at his acclaimed after-school academy, helped by three “burly black men of testicular fortitude”, as he puts it, he has stopped hundreds of disaffected boys spiralling into crime with a regime of army-style drills and classes on everything from how to play the stock market to etiquette. The strategy is so successful that three-quarters of his pupils are aiming at university rather than staring at a stretch inside.

What does he think has caused the explosion of aggression in Britain’s youth? Lewis, who had the pleasure last week of discomfiting Cherie Blair with his straight-talking views on how Britain’s state schools fail boys — “boys”, he told her helpfully, have a “different psychology from girls” — has a ready answer.

“The problem with our young people is ultimately a problem with us. We have feral youth because we have feral parents. Our children are merely a reflection of what we are.”

One of the reasons for the escalation of youth gangs — and there are “thousands” of them nationwide, he warns, sweeping up girls as well as boys — is the collapse of so many of the traditional structures, including the family, that supported young people in their passage to adulthood. Youth clubs have fallen into disuse and the church is no longer the bulwark it used to be.

Oh dear, I’ve only just settled into one of his comfy chairs and I feel as though he’s embarking on a sermon. Long sentences and polysyllables roll from Lewis’s mouth. I look at the wall where Martin Luther King’s photograph hangs under the emblem “I have a dream” and feel my mind starting to wander.

Luckily the flow is interrupted by a trilling telephone. It’s the photographer. Before he lets him in, Lewis turns to me: “What colour is he?” he asks. “Er, white,” I say. “Hmm, I’m in a minority here,” he quips, before bellowing “Yeah” down the phone in a voice so powerful that I jump.

What a strange mix of charm and toughness. The ice is broken and suddenly, beneath the rhetoric, I can see the pragmatism of his arguments. Of course, if children come home from school and their single mothers are out at work, they turn to gangs of children their own age for company. These gangs hang around street corners and deal in drugs and colonise postcodes. These gangs act, Lewis explains, as a kind of alternative family.

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