Jimmy Savile - why BBC Panorama is investigating BBC Newsnight

To the general public, there may be something almost bizarre about the editor of one of BBC journalism's flagships - Panorama - commissioning an investigation into why the editor of another of BBC journalism's flagships - Newsnight - decommissioned an investigation.

Tonight I heard one correspondent on a rival channel describe it as "corporate cannibalism".

But at stake is something the corporation regards as one of its crown jewels - the independence of its journalism.

Any suggestion that news reporters were prevented from broadcasting a story because of its inconvenience to the corporation could undermine the credibility of BBC News.

And so the fact Panorama is able to investigate editorial decisions within the Corporation is seen as evidence of a vital freedom.

Questions about who knew what and when have revealed something of the labyrinthine bureaucratic structures which operate at the BBC.

For a start, the Chinese walls designed to protect the impartiality of its journalism can appear mystifying.

Is it really possible that the man who had agreed to broadcast two Christmas tributes to Jimmy Savile, George Entwistle, didn't want a proper briefing when told of the Newsnight investigation by BBC News director Helen Boaden? Well, actually, yes.

Whether the conversation, conducted at the Women In the Media awards, was really as brief and minimal as suggested remains one of the key questions for the Pollard investigation.

Did the Chinese walls stand firm?

The Newsnight investigative team of Liz MacKean and Meirion Jones worked to Peter Rippon, the programme editor.

He reported to Steve Mitchell, head of news programmes, who reported in turn to director of news Helen Boaden.

The editor-in-chief at the BBC is the director general, at the time, Mark Thompson.

These layers of management have been criticised for stifling journalistic risk-taking at the Corporation, but BBC News is a huge enterprise.

The world's largest broadcast news organisation, it generates around 120 hours of radio and television output every day, as well as online news coverage.

CPS revelations

This scandal shows no sign of abating.

This afternoon the Crown Prosecution Service revealed that in 2009 four allegations of sexual abuse by Jimmy Savile dating from the 1970s were investigated but not pursued.

The CPS says none of the alleged victims were willing to support a prosecution.

Three of the incidents involved girls under 16, two of which were said to have taken place at the Duncroft children's home in Surrey, and one at Stoke Mandeville hospital.

Questions will be asked as to why such serious allegations involving such vulnerable people did not set alarm bells ringing.

With police inquiries and investigations for the BBC and NHS continuing, the sordid wake left by this affair looks capable of tarnishing the reputation of both individuals and institutions.