Imprisonment is so traumatic that 'incidents of self-injury and attempted suicide are inevitable', the Howard League said.
Under legislation included in the Criminal Justice Bill, the Home Office intends to have five private 'secure training centres' built to hold offenders aged 12 to 14.
The centres, which will each contain 40 offenders, were described by the league as an 'extravagant waste of public funds' that would lead to more crime.
The allegations followed the launch yesterday of a House of Lords campaign by the Bishop of Lincoln, the Rt Rev Robert Hardy, to halt the programme. He was backed by the families of some young people who have died in custody. They urged peers and bishops to oppose the plans in the Bill.
Over the last five years, 33 teenagers have committed suicide in prisons and young offenders' institutions.
The Howard League said relatively little was known about the scale of the problem because the Prison Service had only recently started to collect figures on self-mutilation and attempted suicide. The Department of Health, which is responsible for 295 places in secure accommodation, does not collect statistics.
The courts will be able to send those aged 12 to 14 to the new centres under a secure training order for up to a year if they have been convicted of three imprisonable offences and have breached an already imposed supervision order.
Among the deaths in custody highlighted by the Howard League were:
Philip Knight, 15, who was found hanging in Swansea prison in 1990. He had cut his wrists twice before.
Craig Walsh, 15, who was found hanging in his cell at Glen Parva Young Offenders Institution in 1990.
Phillip Beckett, 18, who hanged himself in Leeds jail in 1989. He had been on remand for 96 days, and had threatened suicide.
Frances Crook, the League's director, said: 'The legislation on child jails, and the detailed regime and building specification being given to commercial companies, emphasise security rather than care.'Reuse content