Rogue elements within the intelligence services have been blamed by a senior minister for briefing against the government about the weapons threat posed by Iraq.
Live from the Commons
Key points of Tony Blair's questions and statement in text and video
The Leader of the Commons, Dr John Reid, said journalists were fed false information which accused Tony Blair of exaggerating the size of Saddam Hussein's arsenal.
This fresh development comes as the prime minister prepares to answer questions in the Commons on the lack of weapons of mass destruction (WMD) found in Iraq since the war.
Dr Reid said "a rogue element" or "indeed elements" told journalists Downing Street had doctored the reports to strengthen the case for war against Iraq.
He urged critics to "put up or shut up" as there was "15 years of evidence" that Saddam Hussein had WMD.
The Tories' shadow foreign secretary Michael Ancram criticised Dr Reid's "silly remarks" saying they would "increase the wrangling" over the issue rather than providing the full and swift answers needed from the prime minister.
On Tuesday it was announced an influential group of MPs is set to scrutinise the government's decision to go to war with Iraq.
'Duping the people'
The Foreign Affairs Select committee will focus on the way intelligence information over Iraq's weapons was presented by Mr Blair's administration.
The prime minister is also expected to announce on Wednesday that Parliament's Intelligence and Security Committee will investigate the issue of Iraq's WMD.
Dr Reid told BBC Radio 4's Today programme the "rogue elements" who were tipping off journalists, including the BBC's defence correspondent Andrew Gilligan, were "anonymous".
He said he was amazed that serious news organisations took the word of "such obviously rogue isolated individuals" rather than the leadership of the
"Their position is not known. They have uncorroborated evidence. They were very small in number."
He even suggested the claims could have come from a "man in the pub".
"The tragedy about this is I have the greatest respect for our intelligence services. I know from working with them... that they are courageous, honest, professional, loyal people.
"And it is quite frankly a disgrace that the leadership of these intelligence and security services, from the chairman of the Joint Intelligence Committee, through all of the leaders who sit on that committee, should have had their integrity impugned in the last week by one or two unnamed individuals."
Hilary Armstrong, the government chief whip, is quoted by the Times as saying "skulduggery" was at work in the intelligence services, and acting against ministers.
But Andrew Gilligan claimed no-one had denied that Downing Street had given undue prominence to "uncorroborated" claims that weapons could be activated within 45 minutes - and this had alarmed security services.
"The concern expressed to me, and not just by a single source ... but four people over the last six months in or connected with the intelligence community ... [is] about the misuse of intelligence material by Number 10."
This fresh twist to the row over Iraq's WMD could further fuel calls for a full public inquiry, with Liberal Democrat leader Charles Kennedy describing Dr Reid's remarks as "quite extraordinary".
He upped his call for an independent inquiry, stressing that a judicial probe might be more appropriate.
A wide-ranging inquiry has so far been rejected by Downing Street, but the pressure was increased by the US Congress decision to investigate the intelligence on Iraq arms. Its hearings will be transmitted on live TV.
In the UK, the Intelligence and Security Committee inquiry would take place behind closed doors.
Intelligence and security committee is appointed by and reports to the prime minister, although it prides itself on its independence. It meets behind closed doors.
Foreign affairs committee is a cross-party select committee and meets in public.
Andrew Wilkie, who resigned as a senior analyst at Australia's most senior intelligence agency because he did not believe the evidence justified the war, said in his opinion the US and UK governments "exaggerated" Iraq's WMD capability and its links with al-Qaeda.
Mr Blair has denied accusations that intelligence information was doctored, insisting he stands "100%" by the evidence shown to the public about Iraq's alleged weapons programmes.
Journalists had claimed intelligence sources said the dossier published in September had been "sexed up" by Downing Street.
The prime minister is to make a Commons statement about the weekend's G8 summit in Evian, which was dominated by the issue of WMD.