Warren Hill opened in 1982 to accommodate Cat C Young Offenders in a closed environment. It was part of Hollesley Bay Colony, the other part of the prison being an open Youth Custody Centre/Detention Centre. When the CJ Act of 1991 came into force the population of open Young Offenders dwindled, and in 1992 the open establishment was adapted to accommodate adult category Ds – initially as a minority but the adult population was the majority within the open prison, with Young Offenders occupying one unit.
Warren Hill together with the Carlford Unit (a Section 53 Unit opened in January 2000) went all-juvenile in October of the same year.
In April 2002 though retaining some shared services,

