BBC reporter Andrew Gilligan was the star witness on Tuesday – the second day of the independent inquiry headed by senior judge Brian Hutton into the apparent suicide of government weapons expert David Kelly.
Gilligan, 34, read out interview notes backing his story in May, which claimed that the government "sexed-up" a dossier on Iraq's weapons of mass destruction, published ahead of the conflict.
The probe was ordered by Blair, who has seen his popularity plummet in the polls and who is at risk of serious political damage if the investigation's findings are negative.
Gilligan told the inquiry he had had three meetings with Kelly since 2001, and that during one encounter on 22 May, the scientist had told him the dossier had been "transformed a week before publication to make it sexier".
Kelly reportedly said that most claims in the official dossier were based on two sources, but a claim that Iraq could deploy WMD within 45 minutes was based only on a single source, implying it was less reliable.
Gilligan asked the scientist if the claim could have been made up.
Kelly reportedly replied: "No it was real information, but it was unreliable. It was in the dossier against our wishes".
"You can see the language in the document is actually inconsistent"
The BBC reporter used a newspaper article earlier this year to claim Blair's key aide and media chief, Alastair Campbell, was the man responsible for ordering intelligence officers to beef up the dossier to make the case for war on Iraq more compelling.
The claims have been strongly denied by the government, and sparked a furious row between ministers and the British Broadcasting Corporation, the world's biggest state broadcaster.
Gilligan was asked on Tuesday if it was Kelly who first mentioned Campbell's name.
Gilligan told the inquiry: "It was him, he raised the subject of 45 minutes and he raised the subject of Campbell."
The BBC man said he then sought out a copy of the dossier and analysed a paragraph which dealt with Iraq's chemical and biological weapons programme.
Gilligan said: "I really did think that the language in that (section) had been hardened. You can see the language in the document is actually inconsistent."
Kelly was found with a slit wrist near his home in Oxfordshire, southern England, on 18 July.
His presumed suicide came after he was identified by the government as a probable "mole", and followed hostile questioning at a parliamentary hearing where the scientist denied being the main source of the controversial BBC story.