The Howard League for Penal Reform has called on the government to close all young offenders units and damned them as a "costly experiment".

Its call came after a Home Office study revealed that the young inmates re-offended quickly and in large numbers. The report studied 102 "trainees" who arrived over two years at Medway Secure Training Centre in Kent. Each inmate costs around £125,000 to look after and the centre is run by Rebound, a division of Group 4 security.

Frances Crook, director of the Howard League, said: "These centres are just squandering public money on ineffective care. These children need dealing with imaginatively on an individual basis."