The suicide of Joseph, 16, a phone thief who was a victim of sentencing policy

Five weeks after his 16th birthday, Joseph Scholes was found dead, hanging from the bars of his prison cell.

He was a victim of the determination of the courts and politicians to sweep young troublemakers off the streets.

Despite his youth and extreme vulnerability - his childhood was destroyed by alleged sexual abuse, depression and self-harm - and although there was no suggestion he used violence in his crimes, he received an automatic prison sentence for acting as a lookout in a series of mobile phone robberies.

His mother, Yvonne, was devastated by news of his death. But it came as no surprise. She had repeatedly told anyone that would listen that her son was suicidal. Her pleas for compassion went unheard and Joseph was sent to Stoke Heath young offenders' institution in Shropshire for two years. Nine days into his sentence, he killed himself.

He is one of 25 people aged between 15 and 17 who have committed suicide in custody since 1990. But his family and supporters, backed by penal reformers, have vowed not to let him become another grim statistic and launched a campaign yesterday for an independent judicial inquiry into the circumstances of his death and the system that locks up more teenagers than any western European country.

Joseph had suffered a nightmarish boyhood. He had been allegedly abused from the age of six by a member of his father's family and was caught up in a bitter custody battle when he parents divorced. As he became more disturbed, he received psychiatric help and was put on medication. Three months before his 16th birthday, he tried to kill himself by taking an overdose and jumping from a window. A resulting fight with ambulance staff led to a conviction for affray.

Shortly after being placed in a children's home, he acted as a lookout for a gang of boys and girls who roamed the streets stealing mobile phones. Two weeks before his court appearance, he slashed his face 30 times with a knife. The deepest wound cut through to the bone and his room had to be repainted because of the bloodstains. His appearance at Manchester Crown Court on 26 February last year coincided with an instruction to the courts from Lord Woolf, the Lord Chief Justice, to impose sentences of between 18 months and three years for street crime, except in "wholly exceptional circumstances".

Passing sentence 19 days later, the court decided Joseph was not an exception and, because no place was available in secure local authority accommodation, sent him to Stoke Heath for two years. Initially he was placed under suicide watch but within days was transferred to a single cell. It had "ligature points" that could be used in suicide attempts, reduced observations and no surveillance cameras.

He was also terrified of the prospect of being transferred to one of the prison's main wings. Joseph was found dead on 24 March last year. "My world collapsed on that day," Ms Scholes, from Prestatyn, north Wales, said yesterday. "But it was no surprise. Joseph said that if he received a custodial sentence he would kill himself and he did. We've learnt to our horror this was by no means unique. Time and time again children have been placed in conditions wholly unsuited to them and their needs."

Backing the campaign for an inquiry, Paul Cavadino, chief executive of the crime-reduction charity Nacro, said: "This country has adopted punitive attitudes and punitive sentences that means we lock up more children than any other western European country."

Deborah Coles, director of the pressure group Inquest, told Radio 4's Today programme: "Too much attention is being placed on locking up people without considering that ... [they] are some of the most damaged and vulnerable people in society. If we continue sending them to prison, they will continue to die."

Martin Narey, who is the commissioner for correctional services and was the Prison Service director general at the time of the death, admitted youngsters as vulnerable as Joseph should not be in young offenders' institutions. "I don't think there was any lack of care in Stoke Heath for this boy, but I would have much rather he had been in a local authority home where the proportion of staff to young people is much healthier and where more care could have been given," he said. Mr Narey said an internal inquiry had been completed and its results passed to the coroner and the family's lawyers. The coroner will decide whether to make it public.