BORIS Johnson and Jack Straw put aside party political rivalries to open a new wing at Feltham Young Offenders' Institute last Thursday.
The Tory mayor and the secretary of state for justice visited the new Heron Wing.
The facility is designed to cut youth crime by increasing education, training and counselling for young criminals.
The initiative, which is part of the Government's £100million Youth Crime Action Plan, will see 15 to 17-year-olds who have shown a commitment to change treated differently while inside.
Mr Johnson said: "Some may argue that we are throwing good money at bad kids but they are wrong. The rate of re-offending for youngsters leaving custody stands at a shocking 75 per cent and it costs £55,000 to detain a young offender for a year, so it makes sense both economically and socially to break young people out of the cycle of crime."