Was dead scientist the single source of the fateful BBC report?

David Kelly went to his death fearing that he might be. Alastair Campbell and others in government are "99 per cent" convinced that he was. Geoff Hoon, the Defence Secretary, named him in a letter to the BBC, and somebody leaked his name to the press.

But no one outside the BBC knows whether the dead man was the elusive "source" at the heart of the bitter dispute between the Government and the corporation that has cost a man his life.

When Andrew Gilligan, the BBC's defence correspondent, made his first portentous report on 29 May, he told listeners to Radio 4's Today programme that he had been speaking to "a British official" who was "involved in the preparation" of the dossier on Iraq's weaponry, published by the Government in September last year. The official alleged that the draft prepared by British intelligence had been altered "to make it sexier".

Far from Iraq being armed with weapons that posed an immediate threat, Mr Gilligan's source allegedly believed it was only "about 30 per cent likely" Iraq had a chemical weapons programme in the six months preceding the war.

Mr Gilligan added some details of his meeting with the source in an article he wrote for The Mail on Sunday that weekend. He revealed that they met in a central London hotel, that it was their first meeting for "nearly a year", and that they began their conversation by complaining about the state of the railways.

This article, for the first time, named Alastair Campbell, Downing Street's director of communications, as the individual responsible for the "misinterpretation" of intelligence data.

Mr Gilligan went on to tell the Commons Foreign Affairs Select Committee that the source was a man he had known "for some time" who was "quite closely connected with the question of Iraq's weapons of mass destruction" and "a civil servant in the non-secret part of the civil service as distinct from the secret part".

He also said he was in contact with at least three other people connected with the intelligence community, but drew a distinction between "the specific source for this specific story, which is a single source, and the three other people who have spoken to me generally of their concern about Downing Street's use of intelligence material".

There is no doubt that one of these four people was David Kelly. And he fitted the description of a "civil servant from the non-secret part of the civil service" who met Mr Gilligan in a hotel in central London - the Thistle Hotel at Charing Cross. He also admitted that the suggestion of a 30 per cent likelihood that Iraq had weapons of mass destruction could have come from him.

But Dr Kelly did not recall complaining about the railways, and had not known Mr Gilligan for very long. He also denied authorship of two other allegations in Mr Gilligan's 29 May report.

The Government's September dossier contained the now-notorious claim that Iraq possessed weapons that could be deployed "within 45 minutes of an order to use them". Mr Gilligan alleged that British intelligence had only one source for that claim, and that it was not included in the original draft of the September dossier.

Both these allegations turned out to be true. But Dr Kelly claimed not to know anything about this before the September dossier was written, and for that reason, claimed that he could not be the "specific source" cited by Mr Gilligan.

Asked whether he had levelled that damning accusation against Mr Campbell, Dr Kelly said: "I cannot recall, but that does not mean to say, of course, that such a statement was not made, but I really cannot recall it. It does not sound like the sort of thing I would say."

Despite the discrepancies, the Government persists in believing that Dr Kelly was the "specific source" mentioned by Gilligan. They think the BBC journalist was himself guilty of taking something he had been told in conversation and embellishing it to "make it sexier".

It is an old principle of journalism that reporters do not identify their sources of information until the sources themselves agree to be identified. The BBC is holding to that principle.

The journalist's version

Gilligan's account of meeting his source. This is an extract from Andrew Gilligan's article in 'The Mail on Sunday' on 1 June 2003

The location was a central London hotel and the source was waiting as I got there. We'd both been too busy to meet for nearly a year, but there was no sign this would be anything more than a routine get-together...

We'd discussed the famous Blair dossier on Iraq's weapons at our previous meeting, a few months before it was published last September. "It's really not very exciting, you know," he'd told me. So what, I asked him now, had changed?

"Nothing changed," he said. "Until the week before, it was just like I told you. It was transformed the week before publication, to make it sexier."

What do you mean? Can I take notes? "The classic," he said, "was the statement that WMD were ready for use in 45 minutes. One source said it took 45 minutes to launch a missile and that was misinterpreted to mean that WMD could be deployed in 45 minutes. There was no evidence that they had loaded conventional missiles with WMD, or could do so anything like that quickly." I asked him how this transformation happened. The answer was a single word.

"Campbell." What? Campbell made it up? "No, it was real information. But it was included against our wishes because it wasn't reliable."