Tory leader Iain Duncan Smith has said Tony Blair must apologise for comments made by his spokesman about dead weapons expert Dr David Kelly.
The inquiry into David Kelly's death will start on Monday
Last week Downing Street spokesman Tom Kelly compared Dr Kelly, who apparently committed suicide last month, to fictional fantasist Walter Mitty.
The spokesman later apologised unreservedly for his remarks, which were made off-the-record to journalists, but Mr Duncan Smith said that was not enough.
"The attempt by Tom Kelly to cheapen the record of Dr Kelly off the record, even before his funeral had taken place, was appalling," said Mr Duncan Smith.
"We should not simply allow it to be dismissed as an unauthorised mistake.
"It is what 10 Downing Street has been doing for far too long. Malicious briefings are part of their culture and Tom Kelly was only presenting the agreed counter-attack briefing from Number 10.
"The fault line goes right to the top. It is surely Mr Blair who must apologise."
Downing Street said it had nothing to add to the apology Mr Kelly made last week.
A spokesman said they were waiting for Lord Hutton to conduct his inquiry into the circumstances of Dr Kelly's death.
The inquiry into the events surrounding the weapons expert's death is due to begin questioning witnesses on Monday.
Mr Duncan Smith warned the government not to make "any attempts at political interference" in the inquiry, run by senior judge Lord Hutton.
"Lord Hutton has a reputation for independence and integrity.
"I have every
confidence that he will establish the precise circumstances of Dr Kelly's death
and the role that the Ministry of Defence - or even Downing Street itself -
played in releasing Dr Kelly's name to the media," he said.
Shadow chancellor Michael Howard said Lord Hutton should widen the remit of his inquiry to include "everything we were told in the run up to the war".
He told BBC1's Breakfast With Frost programme that despite the government's "dodgy dossier" the Conservatives would still have supported going to war with Iraq.
""There was no need to lie to gain support for the war.
"We would have told the truth. We wouldn't have misled the House of Commons and we wouldn't have misled the nation."
Lord Hutton has already listed witnesses who will be questioned next week.
First is a friend of Dr Kelly's - Terence Taylor, from the Institute for Strategic Studies in Washington.
He will be followed by Richard Hatfield, personnel director at the Ministry of Defence and Dr Kelly's line manager.
Witnesses to the Hutton inquiry next week:
Richard Hatfield - Personnel director, MoD
Julian Miller - Intelligence and security secretariat, Cabinet Office
Martin Howard - Deputy chief of defence intelligence, MoD
Patrick Lamb - Deputy head counter proliferation department, Foreign Office
Andrew Gilligan - BBC
Susan Watts - BBC
Gavin Hewitt - BBC
Richard Sambrook - BBC
Brian Wells - Director of counter proliferation and arms control secretariat, MoD
John Williams - Press chief, Foreign Office
Other witnesses due to give evidence to the inquiry next week include officials from the Ministry of Defence, the Cabinet Office, Foreign Office and key figures within the BBC.
Dr Kelly's body was found in woods at Harrowdown Hill, Longworth, on 18 July.
The 59-year-old is thought to have committed suicide after being named as the source of stories that raised concerns over the way the government presented its case for war with Iraq.
His funeral was held last week in Longworth, Oxfordshire. It was attended by Lord Hutton and Deputy Prime Minister John Prescott, among family and friends.
An inquest into Dr Kelly's death was opened and adjourned on 21 July at Oxfordshire Coroner's Court.