Government weapons adviser David Kelly had always denied he was the "main source" for the story which claimed Downing Street "sexed up" a dossier on Iraq's illegal weapons.
David Kelly said he wanted Gilligan's views on Iraq
Dr Kelly said he had met BBC defence correspondent Andrew Gilligan a week before the report, which sparked a furious row between the government and the BBC.
But he said he did not see how that meeting could have produced the BBC report about a senior security source's claims regarding the September's Iraq dossier.
Dr Kelly was publicly questioned about the row for the first time by the Commons foreign affairs committee - with some MPs suggesting he was being made a "fall guy".
Committee chairman Donald Anderson wrote to Foreign Secretary Jack Straw saying the MPs thought it "most unlikely" Dr Kelly was the source.
And he said Dr Kelly had been "poorly treated" since admitting he had met Mr Gilligan - a charge strongly rejected by the Ministry of Defence.
The MoD said Dr Kelly had briefed Mr Gilligan a week before his report was broadcast on the Today programme on 29 May.
The BBC has refused Defence Secretary Geoff Hoon's request that it confirm whether or not Dr Kelly was Mr Gilligan's source.
Dr Kelly told the MPs he had first met Mr Gilligan last September and had met him twice since, including May's now infamous encounter in London's Charing Cross Hotel.
That meeting was not designed for Dr Kelly to give information to Mr Gilligan, but instead for the BBC correspondent to give the official his perspective of his recent visits to Iraq.
He said he did not recall their meeting as following the same line as Mr Gilligan's account of his meeting with his main source.
But one part of that account - about a 30% probability of Iraq having chemical weapons - did sound "the kind of thing I might have said", he said.
The Iraq War report has been reopened
"I did not see how on earth I could have been the primary source," Dr Kelly told the MPs. "I could not see how that authority could have emanated from me."
But he realised he might have inadvertently contributed to Mr Gilligan's report, he said.
He said he did not think the intelligence services were unhappy with the final dossier.
Conservative MP Richard Ottaway wanted to know why Dr Kelly had allowed the MoD to put out a statement saying it did not know whether or not he was the BBC's source.
Dr Kelly said that was the MoD's assessment. There were other things that did match what he did say.
He agreed he could not have been the source.
That was because he had not known that a claim that Iraq could launch weapons in mass destruction within 45 minutes had been added to the dossier only weeks before its publication.
Labour MP Andrew Mackinlay suggested the official was a "fall guy" thrown up as a distraction.
Dr Kelly said he could not answer that question, adding that he accepted the process that was going on.
As an expert on inspection of Iraqi weapons' programmes, Dr Kelly said he had written pieces for the dossier in May and June last year.
Those were about the history of inspections and Iraq's deception rather than intelligence material, he said.
Tony Blair's official spokesman stressed the government had always said it could not be certain whether Dr Kelly was the source.
Environment Minister Ben Bradshaw, a former BBC correspondent, said he still thought Dr Kelly was the source.
"If it is not Dr Kelly, I would think this is the perfect opportunity for the
BBC now to say on the record that the source was not Dr Kelly," he told BBC Radio 4's PM programme.
The BBC had nothing to add after the evidence session. A spokesman said: "As we have said before, we are not going to get drawn into discussing sources."
The foreign affairs committee published a report on the case for war in Iraq last week which said the "jury was still out".
But it cleared Downing Street director of communications Alastair Campbell of "sexing up" the dossier.
After Dr Kelly was named, the MPs reopened the inquiry to get the chance to question him.