Under the scheme, the Youth Justice Board (YJB) and the Ministry of Justice (MoJ) gave a consortium of youth offending teams from Hammersmith & Fulham, Kensington and Chelsea, Westminster, and Ealing upfront cash to cut custody use over two years.
The West London consortia, one of four areas to start the project, had a target reduction of 11.8 per cent over the two-year project, which ran from October 2011 to September this year.
But figures released by Westminster Council show that the consortia actually reduced the use of custody by 38 per cent.
The authority has said that the reduction is a result of the work of the pilot.
However, latest youth custody statistics show that there were similar falls in the use of custody across the entire youth secure estate during the same period.
The number of under-18s held in custody fell from 1,991 to 1,249 between October 2011 and September 2013 – an across the board fall of 37.2 per cent.
The exact impact of the pilots are currently being evaluated by experts from Sheffield Hallam University.
Danny Chalkley, lead member for children and young people at Westminster Council, said: “This pilot project tests how local authorities can be more innovative and creative in reducing custody.
“It is a great acknowledgement for all the hard work being undertaken by our staff who work tirelessly in the community to make a difference in the lives of young people.”
Betty McDonald, head of the tri-borough youth offending service covering Hammersmith & Fulham, Kensington and Chelsea, and Westminster, said it is possible to manage most young offenders safely in the community.
“We’re looking at the stages in which young people go into custody, and preventative measures that can be taken to reduce this,” she said.
“We talk to young people about the importance of complying with orders, the reasons they haven’t complied, and the serious consequences if they don’t comply.”
She added that the service has a big focus on parental responsibility.
“We’re drawing on extended family networks and contacting parents to tell them their child will be in custody unless changes are made.”
Lin Hinnigan, chief executive of the Youth Justice Board (YJB), said the pilot had been worthwhile in providing an opportunity to “test out and draw learning from new approaches to youth justice delivery”.
“It is clear that performance has been strong across the tri-borough consortia and I believe the initiative should be justly proud of their achievements.”
West London was one of two areas to complete the two-year project, the other being West Yorkshire.
Two other areas – Birmingham and a group of authorities covering north-east London – pulled out a year early because they recorded increases in the use of custody over the first 12 months of the pilot.
Under the two-year scheme, consortia were held liable for paying back the money if they fail to hit their targets, but by quitting the scheme a year early, Birmingham and the north-east London consortia did not have to pay anything back.
It is not yet clear how West Yorkshire has fared over the two-year period, although an evaluation of the first 12 months of the pilots, published over the summer, showed it achieved reductions in the use of custody of 26 per cent in the first year.