‘When I grew up,” says Bernard Hare, “you got a whack around the ear if you did wrong. But people are scared of kids these days. They think they might get stabbed. Kids are getting more and more out of control.”

He knows what he’s talking about: a former social worker, he’s worked with children for many years. For the past decade or so he’s been closely acquainted with the Shed Crew, a gang of runaways in Leeds whose adventures in drugs, promiscuity and car crime he describes in Urban Grimshaw and the Shed Crew, an extraordinary account of the parallel world of missing children who live under our noses in every inner city, but officially don’t exist.

Anyone with children will be horrified by what Hare has to say: “You get smackheads at 14, though they’re probably experimenting before that . . . The promiscuity is alarming. Many kids lead full, active sex lives from the age of 11 or 12. And the first question these kids seemed to ask about adults they met was, ‘Is he or she a nonce?’ Paedophilia is much more widespread than people realise.”

The boy Hare calls Urban Grimshaw was 11 when they met. Hare knew Urban’s mother, who was a heroin addict and had more or less abandoned him. Urban hadn’t been to school since he was six, couldn’t read or write or tell the time, didn’t know the days of the week, nor the name of the country he lived in. He stole as many as 50 bottles of nail varnish a day — to inhale the solvents they contained. He was living with several other children in someone’s garden shed.

Hare gradually found himself taking responsibility for Urban and the others. But he wasn’t accepted among them till he’d endured a terrifying drive in a stolen car, been scorched by flames as it was set alight (to remove fingerprints), and agreed to be tattooed with a dirty needle.

Hare was a man with time on his hands. He had lost his job as a social worker some years before after being convicted for being drunk and disorderly, and had spiralled into depression and a casual heroin habit. When he lost his income — as “a man with a van” — he supported Urban by shoplifting. So he was hardly the conventional guardian for a needy child, but it was his own flakiness — he was later fined for a string of petty offences — that won Urban ’s trust.

Seeking official help to look after Urban, Hare was rebuffed. Doctors and dentists refused to treat a child with no records. Social services refused benefits. Schools didn’t want to know. “Nobody gave a shit and I was left to cope. I wasn’t sure I was suitable,” he says. “I certainly wouldn’t want any child of mine to be cared for by someone like me.”

But the friendship has turned out to be fruitful for both of them. Hare was taken aback when a friend told him: “I don’t think you realise how much influence you have.” So he cleaned up his act and did his best to be a good role model. When Urban turned 21 recently Hare asked if he could adopt him as his son. Urban agreed.

In person Hare, 47, is dour with an attitude he describes himself as “sod you, up yours”. He doesn’t do drugs any more but smokes endless roll-ups. His car reeks of them as he drives me round East End Park in Leeds where he grew up — and where the shed once stood. The shops have been burnt out. Several homes have metal sheeting over the windows and doors.

“If you came here at night you would see all the kids sitting round doing glue,” he says.

Most people assume that because we have a welfare state it is pretty much impossible for children to fall through the net. Not so. If you are 14, your mum’s a heroin addict and her week’s money has gone to her dealer, you’re on your own.

Such children tend to cluster together and form their own, anarchic society. Like those in conventional society, they seek status and if they cannot get it legally they will get it illegally. “The top twockers on the estate” — joyriders, their name comes from the offence of taking without owner’s consent — “get respect according to how much they wind up the police. One used to drive into the police station, honk his horn and wait till they came out for him.”

After driving me round, Hare returns to his flat in a tower block. Children loiter outside in hoodies, kicking loose stones. Officially and unofficially, Hare has worked with many children over the years. “A new crew every year, each one worse than the one before.”

The Shed Crew have followed a predictable path. The boys have all been in and out of prison; Urban himself is serving time for driving while banned. The girls are mostly single mothers. Only one Crew member has a steady relationship, a steady job and — perhaps most remarkable — a clean driving licence. “Kara is doing the best of everyone,” says Hare.

By chance, Kara, 23, comes round to Hare’s flat while we are talking. She plonks herself down in an armchair and offers cans of beer all round. Like Hare, she believes today’s children are worse than her own generation: “We had more respect for people. I used to go out and get pissed and maybe set things on fire — but I didn’t get old biddies out and happy-slap them. We had respect.”

Hare holds all politicians in contempt and believes the bureaucracy of social work departments is hopelessly unsuited to rescuing some of the children who need help the most.

Like Camila Batmanghelidjh — who runs London’s Kids Company, which cares for similarly dispossessed kids, and whose methods are being assessed for replication by the government — Hare has an unorthodox approach. It may have something to teach us, and the Department for Education and Skills is said to be interested in working with him.

“If it was up to me, I’d close the kids’ homes. And shut down social services. I have no respect for social workers,” he says. “It’s been professionalised. There is no room for working-class people. So social workers are not on our wavelength now. They are in cushy jobs, with long lunch breaks and flexitime. Hopeless.”

Perhaps, but I can’t help wondering if his bitterness has more to do with losing his job. I ask if other people could do what he’s done. “I wouldn’t advise just anyone to do this kind of thing. You’ll get your money taken from you, for a start.

“They don’t suffer fools, these kids. They need limits. They’ll kick against them, but secretly they quite like them. But you can’t just tell them what to do if they don’t respect you.”