Prison vans taking troubled teenagers to Feltham Young Offenders Institute often do not arrive until midnight putting the youngsters at risk, warns a watchdog.

The prisons' independent monitoring board said it had serious concerns about the late arrival of prison vans and has demanded action from Ministers to safeguard the young offenders.

The report said vans were often so late new inmates were put at risk as they do not have enough time for induction and assessment before spending their first night behind bars.

On arrival at Feltham prisoners should be interviewed, risk assessed, told about the prison regime and enrolled on an induction programme.

The chairman of the board Kathy White said: "The prison service has been totally inadequate in enforcing the prison escort service contract.

"Vans are sometimes arriving at midnight with vulnerable 15-year-olds who have never been in custody before. This is completely unacceptable and we have grave fears that it will take a tragic case of self harm or suicide before something is done.

"There must be enough time for the prison staff to carry out thorough and effective assessment and first night inductions."

The board has called for urgent action from the Ministry of Justice.

Serco, which supplies the prisoner transport from courts to Feltham, declined to comment.

The number of deaths in custody nationally has risen and the report pointed out that Feltham faced significant additional risks given its high percentage of foreign nationals, the number of prisoners on remand, and the mental health needs and age of inmates.

Suicide attempts and many more incidents of self harm continue and the board said it regretted there had been no local study to identify predisposing factors that could prevent further incidents.

The governor and staff were praised for the progress they made over the past year in many areas but the board said it remained extremely concerned at the exceptionally high levels of staff sickness.

It agreed with a statement made after a recent inspection by the Chief Inspector of Prisons who said: "Feltham will never be an easy establishment to run. Its spread out site and the volatile nature and short stay of much of its population means that safety can never be taken for granted."

The board is concerned that increasing financial constraints throughout the prison service will put even greater pressure on Feltham this year. The report covers the period from November 2006 to October 31, 2007.