We'll create new youth-crime jail to break cycle of violence

The aim of the unit would be to break the cycle of reoffending by giving inmates positive role models.

But it represents a dramatic break with Conservative criminal justice policy and was disclosed as the Mayor's deputy in charge of policing, Kit Malthouse, spoke of the failure of "the old macho days" of "lock 'em up and throw away the key".

In an outspoken interview with the Standard, Mr Malthouse signalled that a new knife and youth crime strategy being launched on Monday will be a dramatic break with past policy.

He said: "To send a 16-year-old boy to Feltham [Young Offender Institute] for three months might sound like a good idea, but locking him up with hardened criminals just teaches him to become a better criminal and makes things worse. We've got to be smarter than that and so we've come up with a better solution.

"We need to do everything to ensure they are employable as say [apprentice] electricians or engineers when they come out, because every time we lock them up for three months, it costs us £90,000, and every time they reoffend it's harder to pull them back into society."

James Cleverly, deputy leader of the Tories on the London Assembly, said the Mayor was holding talks with the Ministry of Justice to use the renovated Cookham Wood Young Offender Institute in Kent. Alternatively, a separate wing of another prison, segregated from other inmates, could be used.

Currently, a quarter of young criminals with no previous convictions re-offend, compared with 42 per cent of those who have one or two offences behind them.

And 82 per cent of young offenders who have more than 10 previous convictions break the law again. Mr Johnson says he wants to protect first-time inmates who could be tempted into crime if they rub shoulders with repeat offenders in mainstream jails. Instead, they would be given mentors such as teachers, gym instructors and prison officers.

Mr Cleverly told the Standard: "We're going to say to these people: 'This is your opportunity. You can either grab it with both hands and turn your life around, or you've wasted it.' There will be no second chances."

The Mayor is also looking at ways to bring potential employers into the facility to talk about job prospects when young people leave. City Hall hopes the new policy will save taxpayers millions of pounds. The average cost of a career criminal to the justice system is £800,000.

The proposal comes amid fears of escalating violent crime; 27 teenagers have been killed in the capital so far this year compared with 26 last year.

Mr Malthouse attacked youth justice policy going as far back as 1993 when the Conservatives were in power. "You can chart the rise in youth violence back to a single moment, the murder of James Bulger in 1993, after which successive governments took a decision to lock up more and more young people," he said.

"After that, crimes that passed as mischief for generations suddenly became anti-social behaviour and the number of youths imprisoned rose dramatically. We criminalised a whole section of society and along the way we inculcated an intolerance of young people.

"The borough commander in Bromley tells me that when it snows they get four-hundred 999 calls about kids throwing snowballs. This is what it's come to it's crazy!"

On Monday he and Mr Johnson will also announce a further five key measures to tackle the long-term social factors behind youth crime.

"You can correlate kids who are involved in youth violence with underattainment and lack of progression at school, and that's why we have a new initiative to boost literacy and numeracy among vulnerable children," said Mr Malthouse.

"Also, statistically, children in care are more likely to go to prison than to university and we need to address that. There is rather a lot of money being spent on the wrong things, like expensive DJ equipment to turn kids into rappers: we would prefer them to read and write first."

Mr Johnson's plan puts him at odds with national policy. The Tories do not differentiate between first time and repeat offenders and have no specific plans on mentoring in youth offender institutions.

Mr Cleverly said it was crucial to keep ministers onside if the plans were to go ahead: "We have to do it with the goodwill of the Ministry of Justice and don't want to alienate them for the sake of political point scoring."