A report by the Centre for Crime and Justice Studies (CCJS) at King's College London said most youth justice targets had been missed despite a "substantial" increase in spending.

The independent study said: "Targets have been missed with self-reported youth offending remaining stable. All the expenditure and activity to reduce youth crime has had no measurable impact." It added: "Claims of significant success are overstated."

The experts assessed the impact of reforms since the 1998 Crime and Disorder Act which set up the Youth Justice Board - the quango which oversees the way young criminals are punished - and youth offending teams in England and Wales.

They found that since 2000/01, spending on youth justice has increased by 45% in real terms. But targets on reducing re-offending have all been missed, with latest figures showing "little progress", the report said. "The Government has been beset with problems in setting, revising and failing to hit its reconviction targets for children," it added.

Targets on providing accommodation, education, training and employment, reducing substance misuse and improving mental health had also slipped, it said.

CCJS director Richard Garside said: "The Government's decade-long youth justice experiment was a bold attempt to deploy the full force of the youth justice system to tackle problematic and disruptive behaviour by young people.

"This new research suggests that the experiment has largely failed, if reported youth offending is the measure of success. As the Government continues to explore ways to control public spending this research suggests that ever growing criminal justice budgets are unlikely to deliver the long-term or sustainable success."

Deputy director and report author Enver Solomon said: "The Government's record on youth crime and tackling the multiple needs of children caught up in the youth justice system is less impressive than many would have expected following a wide-ranging programme of reform and substantial investment."

A Ministry of Justice spokesman said: "The Government is committed to tackling youth offending and reducing its impact on communities by intervening early with young people to prevent crime and anti-social behaviour. However, there is clearly more work to do and we are pushing forward our efforts to reduce re-offending further, including by launching a Youth Crime Action Plan this summer.