A follow-up documentary to the ITV1 programme which first revealed allegations against Savile airs tonight on ITV1.
Former police detective and child protection expert Mr Williams-Thomas was behind ITV's Exposure documentary about Savile, which aired in October.
In tonight's programme, he claims ITV's investigators have new evidence to show that Savile was a life-long sexual predator.
He said: "In the first programme, we focused on a fairly short time scale.
"Now we're able to show that Savile's offending behaviours spanned four decades and many hundreds of victims.
"This isn't just someone who offended only against 13-, 14- and 15-year-olds. It's someone who offended against 10-year-olds."
The acting Director General of the BBC, Tim Davie, has appealed to past and present staff "to come forward" if they think that can help with the police investigation into allegations against Jimmy Savile. Read more
Dave Lee Travis has been arrested by police working on the Jimmy Savile investigation - find out more on the ITV News site.
Two women came forward and said that he had allegedly groped them.
He has always strenuously denied the allegations.
He is the fourth person to be arrested under Operation Yewtree - but he comes under the category of 'others'. That means although it's connected or comes about as a result of Jimmy Savile inquiry it is not as a consequence of something he did when he was with Jimmy Savile.
Police investigating the abuse scandal surrounding Jimmy Savile have made a further arrest as they revealed the number of potential victims has risen to 450.
A man in his 60s, from Bedfordshire, was held this morning on suspicion of sexual offences and is being questioned.
Scotland Yard said the allegations against him do not directly involve Savile, and are classed under the strand of their investigation termed "others".
So far, around 450 potential victims have come forward and 200 allegations of sexual assault have been made.
This has risen from around 300 possible victims the force were dealing with last month. The vast majority of allegations have been made against Savile. Officers are looking at three strands within their inquiry: claims against Savile, those against Savile and others, and those against others.
The former judge who is leading a BBC inquiry into the Jimmy Savile sexual abuse scandal has launched an appeal for witnesses.
Dame Janet Smith, has called on potential victims, witnesses, people who worked with the TV presenter and senior staff at the time to assist with the investigation.
According to the inquiry's website, the review also wants to hear from people "who were familiar with the culture or practices of the BBC" in terms of "preventing or enabling the sexual abuse of children, young people or teenagers".
The former policeman whose ITV documentary exposed Jimmy Savile as a paedophile, has said he believes the TV star only wanted to work on his hit television shows so he could gain access to children.
The TV presenter and radio DJ was the star of shows such as Top of the Pops and Jim'll Fix It, it's claimed, all with the aim of enabling him to carry out sex attacks on hundreds of victims.
Jimmy Savile's former BBC radio producer Wilfred De’ath who was arrested on suspicion of sexually assaulting a well-known British actress has insisted that he is a victim of ‘mistaken identity’.
De’ath, 75, was arrested at his bedsit flat in Cambridge as part of the police investigation into child abuse by Jimmy Savile.
“Now I realise how Lord McAlpine must feel," he said. Mr De’ath, was held for around five hours at a Parkside police station in Cambridge before he was freed on police bail and taken back to his home pending further inquiries.