ITV1 is broadcasting an hour-long documentary about the star, called Exposure: The Other Side of Jimmy Savile, on Wednesday night.
In it, Sue Thompson, who was a newsroom assistant at BBC Leeds, claims she walked in on Jimmy Saville indecently assaulting a teenage girl in his dressing room in the mid 1970s.
After seeing the footage, Esther Rantzen, the founder of ChildLine, said she now felt a degree of guilt for ignoring "gossip" that surrounded the Top of the Pops and Jim'll Fix It presenter.
Rantzen, who began presenting That's Life in 1973, told ITV1: "I feel that we in television in his world in some way colluded with him as a child abuser - because I now believe that's what he was."
The nephew of the late broadcaster Sir Jimmy Savile has responded to the programme, saying his family is ''disgusted and disappointed'' that allegations his uncle sexually abused school girls have been made when he is no longer around to defend himself.
