Late British television presenter Jimmy Savile was a far more prolific sex offender than previously suspected, a charity said on Monday, abusing children as young as 2 and targeting victims in a high-security psychiatric hospital.

Savile, a major BBC celebrity and charity fundraiser in the 1970s and 1980s, was unmasked after his death in 2011 at age 84 as one of Britain's worst sex offenders. He preyed largely on children at hospitals and BBC premises, relying on his celebrity status to deter or block any complaints.

The revelation shocked Britain and plunged the publicly funded BBC into crisis. A 2012 report cleared BBC bosses of covering up allegations against Savile, but a police watchdog report last year voiced concerns about police mistakes.

It prompted a wider inquiry into sex crimes by aging showbusiness figures, with 17 arrests made and Australian entertainer Rolf Harris on trial on 12 indecent assault charges.

Research by the National Society for the Prevention of Cruelty to Children showed on Monday there had been at least 500 reports of abuse by Savile, compared with a suspected 140, with most victims aged 13 to 15 but the youngest just 2.

Peter Watt, the NSPCC's director of child protection, said there was no doubt that Savile was one of the most, if not the most, prolific sex offenders that the charity had come across.

"He was manipulative, arrogant and controlling. ... Savile escaped justice because people didn't want to hear or believe what children were saying," Watt said in a statement.

Watt said it was incredible that people were still coming forward more than 60 years later to report Savile, an eccentric character famed for his long blond hair, cigars and penchant for garish outfits and flashy jewelry.

He said Savile, who presented various TV shows including Top of the Pops and Jim'll Fix It as well as supporting a list of charities, started as a predatory sex offender when he was in his teens and continued into his 80s.

The new NSPCC figures, commissioned for BBC show Panorama, were to be broadcast along with details of confidential Department of Health documents showing the extent of Savile's influence over the psychiatric hospital Broadmoor.

Savile became involved with the hospital through a charity in the late 1960s and was later given his own keys and a house on the grounds. Thames Valley police said they had received 16 reports of abuse by Savile inside Broadmoor.

The West London Mental Health NHS Trust, which now runs Broadmoor, told the BBC it would be premature to comment on specific allegations against Savile while a joint investigation by the NHS Trust and the Department of Health was in progress.

The Panorama investigation also found the BBC had launched an inquiry into allegations of inappropriate behavior at the broadcaster in the 1970s but advice about supervising youngsters coming to see Top of the Pops was not acted upon.

A BBC spokesman said the corporation was "appalled" at Savile's crimes and was awaiting a review by former Court of Appeal judge Janet Smith that is considering the culture and practices of the BBC during the years of Savile's fame.

Lawyers representing around 140 of Savile's victims have started legal action in London to seek compensation from a charitable trust set up in Savile's name after his death.