The BBC Director-General, George Entwistle, will be fighting for his career today as MPs demand to know how much he knew about the suppression of a Newsnight investigation into sexual abuse by Jimmy Savile and why he sanctioned tribute programmes to the late BBC presenter.

Just 37 days into his tenure, Mr Entwistle finds his position further damaged by the intervention of the Prime Minister, who expressed concern over the BBC "effectively changing its story", after it yesterday suddenly denounced a blog by the Newsnight editor, Peter Rippon, which had been the Corporation's official version of events for the past three weeks.

The BBC said Mr Rippon was "stepping aside" from his role "with immediate effect" as it admitted "errors" in the BBC website blog, hours before a damning Panorama documentary last night that exposed the way the BBC has handled the Savile scandal. Panorama conducted interviews with two Newsnight journalists who contradicted claims by Mr Entwistle and other senior BBC figures that their story had been intended only as a narrow piece on Surrey Police's treatment of Savile – rather than an exposé of claims of sexual abuse against the former star.

Reporters Meirion Jones and Liz MacKean said that they had been conducting a wide investigation into child-sex abuse by Savile. Ms MacKean said the story was quashed following "an abrupt change of tone" and Mr Jones claimed that "we weren't asked to get more evidence… we were told to stop working on the story". Their claims will fuel suspicion that Mr Rippon was put under pressure by more senior colleagues to kill the story.

Mr Entwistle today gives evidence before the House of Commons Committee on Culture, Media and Sport. Its chairman, John Whittingdale, was damning yesterday, saying: "The handling of this by the BBC has been lamentable, they have made a bad situation even worse and ultimately the Director-General is responsible for that and certainly we would want to press him on that whole issue."

MPs will question Mr Entwistle over why he sanctioned a tribute programme on Savile after the director of BBC News had informed him weeks before that Newsnight was investigating the late presenter. "It seems to me extraordinary that, given George Entwistle was told, that he did not want to know a lot more about it," Mr Whittingdale said yesterday.

The Crown Prosecution Service said yesterday that it had looked into four claims of sexual assault made against Savile following a two-year investigation by Surrey Police in 2009 while he was still alive. Savile was questioned under caution but no charges were made against him as the witnesses were not prepared to testify in court.

It also emerged in Panorama that the BBC did not pass on evidence gathered by the Newsnight investigation to the police. It is only the recent revelations that have seen one of their sources, Karin Ward, interviewed by the Metropolitan Police.