Ian Brady was allowed to come into contact with vulnerable boys at
Wormwood Scrubs prison despite one alleging he had sex with the moors murderer, newly released files show.
The child killer interacted with young borstal inmates for more than five years, the records are said to reveal.
The BBC said it had seen Home Office files that showed Brady also received support from Lord Longford, a former Labour cabinet minister and penal reformer.
Brady was transferred to Wormwood Scrubs in 1974, eight years after he was convicted of the murders of Lesley Ann Downey, 10, and Edward Evans, 17 - two of the five youngsters he killed with girlfriend Myra Hindley.
After being placed on the segregation unit the killer is said to have gone on hunger strike, to force officers to move him and allow him to associate with other prisoners, and he was eventually placed on the prison's Mental Observation Landing.
At the time boys from Feltham Borstal were reportedly sent to Wormwood Scrubs Hospital if they were suffering from mental health problems.
Some of them were as young as 15, a similar age to some of the Moors Murders victims.
Despite eventually regaining weight Brady was allowed to stay on the wing.
A record from September 1976 shows suspicions had been raised by his "unusual interest in any adolescent inmate" and staff had to move the boys away from him.
In December 1977 Brady reportedly wrote to Lord Longford to complain that the prison's principal medical officer had told the governor he should return to segregation. The child killer remained on the wing.
In March 1978 the prison's senior medical officer (SMO) is said to have expressed concerns about Brady's residence in the hospital and his contacts with vulnerable prisoners.
Brady was reportedly allowed to watch television with other inmates and given duties including cleaning toilets and showers.
He is said to have lost his duties in autumn 1981 after a young person reported that Brady had had sex with him.
He was moved to Parkhurst on the Isle of Wight the following year.
Frances Crook, chief executive of the Howard League for Penal Reform, said Brady's high-profile support contributed to an "extraordinary set of circumstances".
She told the BBC: "What happened, and what he did in prisons, I think, is not extraordinary. Actually, I think it happens and has happened every day for years, and is still happening."
A Ministry of Justice spokesman said: "There have been huge changes in the criminal justice system in the last 40 years and allegations of sexual assault are taken extremely seriously and reported to the police.
"Boys under 18 are placed together in youth custody and those aged between 18-21 are held either in young offender institutions with their own age group, or in designated cells or wings in the adult prison estate.
"We are conducting a review into safeguarding in the youth estate to further improve the welfare of those in our care."