What's the story, I asked. I was taken aback by the reply

With the David Kelly affair still dogging the Government last week, it seemed the most obvious thing in the world to ring Tom Kelly, the Prime Minister's official spokesman, to get Downing Street's latest assessment.

My intention was simple. As the Hutton inquiry prepared to open, I wanted to get an inside account of what No 10 felt were the circumstances that led to Dr Kelly's death.

The most legitimate approach was to go straight to the top. "What's the real story of the Kelly affair?" I wanted to know.

To be fair to Tom Kelly, he did preface his remarks by saying that, of course, it was up to Lord Hutton to determine exactly what had happened. Fine, that's precisely what I'd expect him to say. He suggested that one of the "key issues" for Lord Hutton's inquiry would be whether Dr Kelly in any way contributed to his own downfall.

But beyond that preamble, Mr Kelly's first use of the phrase "Walter Mitty" was immediate. "The guy was a Walter Mitty," he said. Of course, I was taken aback by the description and what seemed to be a clear attempt to portray the MoD civil servant as a fantasist. Nevertheless, I continued to hear what was turning into a narrative sequence.

Mr Kelly went on, indicating his namesake had said far more than he should have, that he had become "very worried" about what he had said and subsequently "said not quite the truth to the MoD".

Dr Kelly "thought he was being clever" in his replies to the Foreign Affairs Select Committee, the spokesman suggested. But the scientist panicked when he discovered Andrew Gilligan was being recalled to appear before MPs.

Tom Kelly did not deliver some kind of "menu of options" as has been suggested. He did not appear to be "mulling over the possibilities" as others have said. He may well have done so to other reporters but his remarks to me were presented as a chronological version of events from Downing Street's viewpoint.

Most importantly, at no point was I told by the spokesman that his words were not for publication. But as the briefing was on a background basis, in line with normal lobby practice I decided to conceal his identity. The Independent described him as a "senior Whitehall source". It seemed clear to us that Mr Kelly was revealing something he wanted "out there" but without any Government fingerprints attached to it.

It is worth pointing out that this modus operandi is second nature to Lobby reporters. Virtually every day, we are given information by MPs, ministers, special advisers, press officers and so on. It's our job to sort out the gossip from the facts, the spin from the actual story. Off-the-record briefings will always continue because they allow politicians to suggest, imply and insinuate as they operate in the grey world of "non-attributable" briefings.

Some suggest there can be no such thing as a totally private conversation between the Prime Minister's official spokesman and reporters.

I wouldn't go that far, and, like many journalists at Wesminster, I have repeatedly respected the confidentiality of conversations both with Mr Kelly and his fellow spokesman Godric Smith.

The point about the "Walter Mitty" remarks was that they were in response to a straight question. Crucially, they were repeated not just to me but to other reporters. That's not the sign of an off-the-cuff comment or throwaway line. It's the mark of a well-thought out briefing aimed at influencing the press.

Furthermore, Tom Kelly is not some ingenue who doesn't know how Westminster works. He's a well respected civil servant who was brought in precisely because of his background as an experienced journalist.

It appears that The Independent's cardinal sin was to realise it had a story on its hands.