A parliamentary committee on Monday criticised Blair for publishing an unreliable intelligence document known as the "dodgy dossier".
In its report, the Foreign Affairs Select Committee also expressed concern that no weapons of mass destruction had been found during and after the invasion.
Blair's chief spin doctor and adviser Alistair Campbell also came under renewed fire by the committee which said it had "serious concerns" over several issues although it exonerated ministers saying they did not mislead Parliament.
Cook attacks Campbell
However the report reveals that Campbell should not have chaired a key intelligence meeting and committee members said they concerned that, as a result, Blair had no direct access with the Joint Intelligence Committee.
There were also "serious concerns" over the dodgy dossier's claims that Iraq had tried to procure Uranium. Committee members concluded the dossier was in fact made up of 90 per cent non-intelligence, most of which had been lifted from the Internet.
Hours before the committee revealed its damning findings, former House of Commons leader Robin Cook launched his scathing criticism of Campbell, in The Guardian newspaper.
Cook, who resigned from the Cabinet opver the decision to attack and invade Iraq, said that Campbell was using an ongoing BBC row to divert attention from Tony Blair's troubled justification for war.
"He has managed to convince half the media that the foreign affairs inquiry is into the origins of his war with Andrew Gilligan (BBC journalist), not in to the war with Iraq," said Cook.
"The serious allegation is that they got it wrong, and they should not be allowed to get off answering that issue because Alastair has souped up this controversy." The "spat" between Gilligan and Campbell was also referred to by the parliamentary committee which said it felt the BBC journalist's sources "proved to be credible".
Blair to aide’s rescue
The prime minister told a Sunday newspaper that the claim Campbell "sexed up" the dossier was "about as serious an attack on my integrity as there could possibly be".
|Campbell comes under renewed|
fire over Iraq dossier row
He is bound to be embarrassed by the content of Monday's report.
A leaked letter last week revealed that Campbell did suggest 11 changes to an intelligence report six months before the war.
Dodgy dossier full of errors
Blair himself will appear before a separate parliamentary committee on Tuesday when he is expected to be grilled about the September dossier and a second so-called dodgy dossier, published in February.
The February dossier was lifted from a student thesis – information that was 12 years out of date and kept all the student's spelling mistakes and grammatical errors.
Only the word “terrorist” was added to the thesis in an attempt to spice up the impact on the British public.
The failure to find any such weapons in Iraq has undermined the Labour government's credibility and damaged Blair's popularity and poll ratings.