Sir David Ramsbotham said the willingness of the privately-run prison to accept all categories of prisoners had been "taken advantage of" by the Prison Service.

As a result the jail, built to house 771 prisoners but holding 1,044, was in charge of an unprecedented mix of juveniles, young offenders and adult prisoners.

The situation had led to a deterioration in conditions and treatment of prisoners, he said.

The jail has the highest suicide rate of any in England and Wales. There have been 11 deaths in the past five years.

Facilities 'inadequate'

In the report, carried out following an unannouced visit, Sir David expressed concern that juveniles could come into contact with adult prisoners - and he concluded that facilities were inadequate for young people to be held there.

In the segregation unit, inspectors found a 16-year-old in a cell next to an adult prisoner who was a known hostage-taker.

Overall he praised the establishment, saying it was well-run with a number of good practices including good staff relations with prisoners, an anti-bullying strategy, health care provisions and a suicide awareness scheme.

He said the jail offered good value for money and staff there should feel proud of their achievement.

The new Director General of the Prison Service, Martin Narey, welcomed the report.