A study by the NSPCC, commissioned for the BBC's Panorama, reveals confidential documents examining the extent of Savile's offending and his unprecedented access to Broadmoor hospital, where some of his abuse took place.
The report said the scale of Savile's offending inside Broadmoor is higher than previously thought, with Thames Valley Police having received 16 reports of abuse by him inside the special hospital.
It also describes how some awe-struck civil servants erroneously referred to the Top Of The Pops presenter as "doctor", unaware of the trauma he was inflicting on some youngsters behind hospital doors.
The figures show the most common age group for Savile's victims was 13 to 15 - and the youngest alleged victim was just two years old.
Peter Watt, the NSPCC's director of child protection, said: "There's no doubt that Savile is one of the most, if not the most, prolific sex offender that we at the NSPCC have ever come across.
"What you have is somebody who lost no opportunity to identify vulnerable victims and abuse them."
The joint BBC investigation between Panorama and The World At One, which airs today on BBC One and BBC Radio 4, asks how the DJ got so close to the heart of Britain's establishment, and why in 1972 the BBC failed to take effective action that might have saved young people from abuse.
Trevor Smith, a former Broadmoor manager and former branch chairman of the Prison Officers' Association, said he remembered seeing Savile at a hospital charity day, exchanging kisses for autographs from young girls.
He told the programme: "He (Savile) kissed these girls who were about 13 smack bang on the lips, held his hand behind their neck to pull them forward and he virtually was giving them French kisses."
One of Savile's alleged victims said she was targeted by the veteran entertainer at a BBC talent audition as a 14-year-old in 1971.
She said: "He reassured me by putting his arm on my shoulder and rubbing my arm, and then he gave me a cuddle and so he was touching my breasts, and he kissed me and he tried to put his tongue in my mouth."
l Savile: The Abuse Of Power is on BBC1 at 8.30pm today.