An expert panel found in an internal report that Joseph Scholes’s problems were so great that the institution could not provide the care that he needed.

His mother, Yvonne, yesterday joined children’s charities and prison reform groups in calling for a public inquiry into the boy’s death in March last year. Mrs Scholes said that her son was too immature and vulnerable to be sent to the institution after he admitted being part of a gang that stole mobile phones.

Joseph, who had a history of mental problems, was sentenced to two years at Stoke Heath young offender institution for robbery. Nine days into his sentence he hanged himself. Mrs Scholes said: “He had told everybody concerned that he would kill himself if he received a custodial sentence. The judge commented on it at the trial, yet he still sent him to an unsafe environment. It was nothing less than a death sentence to Joseph.”

Mrs Scholes, from Prestatyn, North Wales, and her MP, Chris Ruane, went to Westminster yesterday to press for an inquiry.

Paul Cavadino, the chief executive of the crime reduction charity Nacro, said: “This shocking case demonstrates why a vulnerable child should never be held in Prison Service accommodation. Most juvenile offenders should be dealt with by supervision in the community. The small minority who need to be detained should be in local authority secure units, which have higher staffing ratios and regimes more suitable for vulnerable and disturbed young people.”

The Home Office ruled out an inquiry into Joseph’s death. Lord Woolf, the Lord Chief Justice, had told mobile phone theft gangs that they would be sent to prison, apart from exceptional circumstances.

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