The BBC's acknowledgement that Dr David Kelly was its source has precipitated a crisis which goes right to the top of the organisation.
By Nick Higham
BBC media correspondent
Opposition MPs have queued up to accuse the BBC of irresponsibility, of being partisan, of being obsessive in its defence of a questionable story - and there have been calls for the resignation of senior figures up to and including the chairman of the BBC governors, Gavyn Davies.
For an organisation which sets great store by its reputation for accuracy and impartiality this is potentially immensely damaging.
It helps to explain why, ever since Andrew Gilligan's controversial report was broadcast on the Today programme on 29 May, the BBC has so steadfastly resisted government pressure to retract or apologise.
There is simply too much at stake.
David Kelly faced MPs days before he died
Lord Hutton's judicial inquiry into the circumstances surrounding Dr Kelly's death is likely to ask a series of pointed questions about the corporation's role.
Firstly, what exactly did the BBC report?
Andrew Gilligan described his source as a British official who was involved in the preparation of the government's first intelligence dossier on Iraq's weapons.
He said the source told him the dossier had been transformed to make it sexier, at the behest of Downing Street.
Mr Gilligan has now issued a statement insisting that he did not misquote or misrepresent Dr Kelly, and pointing out that the weapons scientist had expressed similar concerns about Downing Street's interpretation of intelligence to the BBC's Newsnight.
Newsnight's report was prepared by Susan Watts and transmitted four days after Mr Gilligan's. Her source too, it now turns out, was Dr Kelly.
She described him as a senior official intimately involved in pulling together the dossier. He told her, she said, that the dossier's insistence that there was an imminent threat from Iraq was a Downing Street interpretation of the available intelligence.
And he said there'd been an argument between the intelligence services and Number 10 over the claim that Iraq could make weapons of mass destruction ready within 45 minutes. The statement had been taken out of all proportion.
The government and its director of communications Alastair Campbell took fierce exception to these claims.
The prime minister himself argued that they questioned his credibility and implied that he had deliberately misled the British people to persuade them to go to war.
The government's fury was increased when Mr Gilligan wrote an article for the Mail on Sunday - after his Today report went out, but before Susan Watts' report on Newsnight was transmitted.
In it he said he had met his contact at a central London hotel (later revealed to be the Charing Cross Hotel). And for the first time he named Alastair Campbell.
The BBC has been accused of being "obsessed" with Alastair Campbell
When asked how the transformation of the dossier had come about, he wrote, his source answered with a single word: "Campbell".
So the second question is: was the original Gilligan story right?
The BBC's governors certainly thought so. They backed the decision to broadcast both the Today and Newsnight stories, though in doing so they gave further ammunition to the BBC's enemies when they spoke of "stories based on senior intelligence sources".
Dr Kelly was not an intelligence source - but then neither of the original reports had described him as one.
But the governors' backing did not extend to the claim in the Mail on Sunday about Mr Campbell's role - and indeed an embarrassed corporation announced it was looking again at the rules under which reporters and presenters write for the newspapers.
The BBC's support for Mr Gilligan was bolstered by the fact that Ms Watts' report was so similar.
Either the same source had briefed both, in which case Mr Gilligan's account of what was said could be independently corroborated, or (even better) there were two different sources.
For the BBC the fundamental question is still this: did the two journalists accurately report what Dr Kelly said?
But Downing Street was insisting the central allegations were wrong.
At one point the BBC considered accepting that its source may have been mistaken, even if its reporting of what he had said was accurate.
In the end no retraction was forthcoming.
The foreign affairs select committee, which had interviewed Mr Campbell, Mr Gilligan and Foreign Secretary Jack Straw among others, were divided on party lines on the question of what role Mr Campbell had played in the compilation of the dossier, and concluded that the 45 minute claim had not warranted the prominence it was given.
And there the matter might have rested had the Ministry of Defence not announced that one of its officials had come forward, saying he believed he might have been Mr Gilligan's source.
That raises a third question. Why, when invited by the MoD to confirm that Dr Kelly was its source, did the BBC refuse?
The answer was one many journalists will recognise.
The BBC argued that the journalist's sources had to be protected - and when, after Dr Kelly's death, it finally admitted his role, it reaffirmed that it had owed him a duty of confidentiality while he lived.
MPs questioned Mr Gilligan and Mr Campbell about the dossier
Unauthorised sources like Dr Kelly risk disciplinary action or worse if their identity becomes known - his death is a terrible reminder to all journalists of the tragic consequences that can follow when a source's anonymity is compromised.
Without a guarantee of anonymity few sources would be willing to take the risks of leaking secrets.
Yet some of Dr Kelly's friends argue that if the BBC had named him earlier he might still be alive.
As it happened his name was soon published. Within a day Dr Kelly's name had been leaked to the newspapers.
Soon, clearly uncomfortable, he was wheeled out to give evidence to the foreign affairs committee, where he admitted talking to Mr Gilligan and Ms Watts but denied saying some of the things attributed to him.
He did not believe, he said, that he could be the BBC's main source.
That raised a host of further questions. Had Mr Gilligan and Ms Watts misquoted him? Rather than Downing Street "sexing up" a dossier, was it Mr Gilligan who had "sexed up" what his source had told him?
Or had Dr Kelly said one thing to the journalists but, under pressure once his cover was blown, said something quite different to his bosses at the MoD and the foreign affairs committee - perhaps realising that he had gone too far in his briefing?
Dr Kelly's friend, the former Panorama reporter Tom Mangold, said Dr Kelly would not have known about Downing Street's involvement in compiling the dossier.
The BBC, he said, should produce substantive evidence to back its claims.
For the BBC the fundamental question is still this: did the two journalists accurately report what Dr Kelly said - even if Dr Kelly himself later denied saying it to the foreign affairs select committee?
But of course there is a wider question as well. If he did say what Mr Gilligan and Ms Watts alleged, was Dr Kelly right?
That is something Downing Street and Mr Campbell have always disputed.