Media playback is unsupported on your device Media caption The former Top Of The Pops and Jim'll Fix It presenter died in October 2011

There have been at least 500 reports of abuse by ex-BBC presenter Jimmy Savile, NSPCC research for Panorama has found.

Most of the alleged victims were between the ages of 13 and 15, but the youngest was two.

Meanwhile, leaked memos reveal the extent of Savile's influence at Broadmoor psychiatric hospital, where he was appointed to lead a task force to reform the hospital.

Panorama has been told about 16 reports of abuse at the hospital.

The Department of Health and the BBC are due to publish reports into Savile later this year.

Children's charity the NSPCC said its helpline had received 50 more reports of abuse by Savile since its joint report with the Metropolitan Police was published in January 2013.

These included reports from victims themselves, people who knew victims of abuse and people reporting information which was considered useful to the ongoing investigations.

Media playback is unsupported on your device Media caption Shelley Jofre reports on how Jimmy Savile was able to gain influence at Broadmoor psychiatric hospital

The earliest incident dated back to the mid-1940s, with the most recent in 2007.

The report says most of the abuse took place on BBC premises, in hospitals and at children's homes.

Peter Watt, director of child protection at the NSPCC, told BBC Breakfast Savile saw himself as "immune".

He added: "Behind these statistics are individual children whose lives were ruined by a man who was an opportunistic sexual predator."

Broadmoor allegations

Meanwhile, a joint investigation by Panorama and Radio 4's the World at One has seen confidential memos which reveal how Jimmy Savile took control at Broadmoor in 1988. He was recommended by a senior civil servant to lead a task force to reform the hospital.

His appointment was approved by Edwina Currie, when she briefly had responsibility for Broadmoor as health minister in 1988.

Confidential government documents obtained by the BBC reveal that civil servants referred to Jimmy Savile as "Dr Savile" and said that he was going through Broadmoor "like a dose of salts".

Mrs Currie told the BBC: "Our efforts to try to improve matters at Broadmoor came up against a very severe brick wall. And it was the senior civil servant in charge of Broadmoor who thought he might be able to do something. Bear in mind Savile had been in and out for donkey's years. So why not ask if he could help to improve matters?"

Panorama: Find out more Image copyright bbc Shelley Jofre presents Savile: The Power to Abuse

BBC One, Monday 2 June at 2030 BST Then available in the UK on the BBC iPlayer

At the time Savile was appointed, the Prison Officers' Association at Broadmoor had just voted to take industrial action, but the documents show Savile thought he could deal with the dispute.

He told Mrs Currie he had discovered some staff were sub-letting hospital housing and fiddling their overtime claims.

"He made it quite clear, he told me, that he would use that against the staff if they misbehaved and didn't call off the overtime ban," she said. "I made a note of it at the time because I was so surprised."

Mrs Currie said there were no complaints about Jimmy Savile at the time. The BBC has learned that there have now been at least 16 reports to the police of abuse by him at the hospital.

Dr Chandra Ghosh, who was a senior psychiatrist at Broadmoor, said she understood why more people had not made official complaints.

"These were people that nobody believed. So if they had in fact turned round and said he had abused them or raped them, nobody would have believed them. You know, this was Mr Savile, you know, Jim'll Fix It," she said.

The BBC has spoken to a woman who was invited to Broadmoor by Savile to sing for patients as a 14-year-old. She says Savile indecently assaulted her at the hospital.

The woman, who does not want to be identified, said: "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. It was the most scariest experience I think of my life. It was a very scary, horrible place."

West London Mental Health NHS Trust - which now runs Broadmoor - expressed sympathy for any victims but said it cannot comment while its joint investigation with the Department of Health is ongoing. It says any complaints involving Savile are part of that investigation.

The Department of Health is investigating 33 hospitals' links with Savile. Reports are expected to be published shortly. The BBC's inquiry is due to be published in September.

Panorama - Savile: The Power to Abuse is on BBC One on 2 June at 20:30 BST.