However there are no plans to close any of the three Secure Training Centres set up especially to house young tearaways in a crackdown on juvenile delinquents.

Lord Warner, head of the Youth Justice Board which takes over responsibility for buying secure places for juveniles from Saturday, said the sort of offenders sent to STCs was likely to shift as reforms came in.

The priority would be to house youngsters as close to their homes as possible.

As fewer 12 and 13-year-olds were sent to the three centres, spaces could be used to house teenage girls who were currently sent to adult prisons because there was nowhere else to put them.

But Frances Crook, of the Howard League penal reform group, which has bitterly opposed the introduction of child jails, said if they were unsuitable for young boys, they were also totally inappropriate for teenage girls.

She said: "I think the government should just throw up its hands and admit that STCs have been an expensive failure and really they should be wound down."

She also expressed dismay at the number of secure places provided by the youth justice board - 3,300 - and said it should make it a priority to reduce the number and focus on community sentences instead.

However two other centres have opened since - Rainsbrook in Warwickshire and Hassockfield in County Durham, providing space for around 120 detainees altogether.

Lord Warner said under the shake-up in youth justice, older children could be sent to the STCs.

Places would have to found for between 90 and 100 girls under 18 who currently end up in adult prisons.

The board has also bought places in local authority secure units and juvenile centres run by the prison service.