The Prime Minister's official spokesman Tom Kelly apologised today for describing the dead Iraqi weapons expert Dr David Kelly as a "Walter Mitty character."
Tony Blair faced calls to sack him over the briefing about events leading up to Dr Kelly's apparent suicide.
Mr Kelly denied trying to discredit the former weapons inspector but admitted the briefing was a "mistake".
He said in a statement issued by Number 10: "I, therefore, unreservedly apologise to Dr Kelly's widow and her family for having intruded on their grief."
Dr Kelly was found dead last month after being named as the prime source for BBC reports that intelligence on Iraq was "sexed up".
Mr Blair called for "respect and restraint" while an inquiry headed by Lord Hutton investigated his death.
But Dr Kelly was described as a "Walter Mitty" fantasist by a senior Downing Street official, The Independent reported yesterday.
Tom Kelly confirmed today that he used the term but insisted it was not an attempt to smear the former weapons inspector.
He said in a statement issued by Downing Street: "We have sought to keep briefing to a minimum in accordance with the Prime Minister's wishes.
"I deeply regret, therefore, that what I thought was a private conversation with a journalist last week has led to further public controversy.
"That was not my intention, nor, most emphatically, was I signalling a Government strategy aimed at discrediting Dr Kelly, as I have explained to the Deputy Prime Minister.
"What I was trying to do, at the request of several journalists, was to outline questions facing all the parties that the Hutton inquiry would have to address, but to do so in a way that made it clear that it was for the inquiry to reach its judgment on the conflicting evidence before it, not me, or the Government.
"It was in that context that the phrase 'Walter Mitty' was used, but it was meant as one of several questions facing all parties, not as a definitive statement of my view, or that of the Government.
"We were discussing questions, not answers.
"I now recognise that even that limited form of communication was a mistake, given the current climate.
"I, therefore, unreservedly apologise to Dr Kelly's widow and her family for having intruded on their grief."
Mr Kelly's comments, ahead of Dr Kelly's funeral tomorrow, sparked fury among friends and former colleagues.
The Prime Minister was warned that his own "credibility" was on the line as he faced calls to act.
Former Labour minister Glenda Jackson said Mr Kelly should be sacked if he had made the "unspeakable" remarks.
She told the BBC Radio 4 Today programme: "Number 10's capacity to disgust us would seem positively boundless.
"We are in a situation where a man has lost its life, his family has been deprived of a husband and father and it would seem that Number 10 is determined to take away his reputation. They are unspeakable.
"That this kind of smear tactics should be coming out of Number 10 at this time is beneath contempt.
"It is to me beyond belief that someone who is the Prime Minister's official spokesperson should be engaging in a conversation on this level about a man who has so recently and tragically lost his life.
"In my view, he should lose his job. I don't think he should be afforded the luxury of resigning - I think he should be sacked."
Mr Kelly, a former BBC journalist is one of two official spokesmen who took over daily press briefings from Alastair Campbell after the last election.
A father of four in his mid 40s, he joined Downing Street from the Northern Ireland Office, where he was director of communications.
Mr Kelly was expected to take a more prominent role when fellow official spokesman Godric Smith leaves Number 10 soon.
Mr Campbell is also set to quit as communications director after the Hutton inquiry into Dr Kelly's death.
*In a separate development, Lord Hutton rejected pleas by broadcasters to be allowed to televise the inquiry proceedings,
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