The British public was not misled over the threat of Iraq's weapons of mass destruction, Prime Minister Tony Blair has insisted.
The focus of the MPs' debate will be the FAC report
He said he stood "entirely" by what was contained in the government's September dossier on Saddam Hussein's weapons, as MPs pressed him to say whether he had "duped" the public over Iraq.
Amid rowdy scenes in his last question time before Parliament's long summer recess, Mr Blair said the BBC should say whether or not government weapons adviser David Kelly was the source of its report that Downing Street "sexed up" the dossier on Iraq's illegal weapons.
Conservative leader Iain Duncan Smith told Mr Blair that unless he sacked his press chief Alastair Campbell "nobody will believe a word you say".
Liberal Democrat leader Charles Kennedy said the only way "to get to the bottom of this" was for the prime minister to order an independent inquiry.
MPs later voted by 299 to 200 against calls for a judicial inquiry. The government's majority was cut to below 100, although several MPs stayed away from the vote.
Foreign Secretary Jack Straw insisted a judicial inquiry was not necessary and revealed that he and Mr Blair had given evidence to the Commons intelligence and security committee on Tuesday.
The committee is conducting its own inquiry on the case for war behind closed doors.
The inquiry call was reiterated by shadow foreign secretary Michael Ancram in a Tory-initiated set-piece debate about the justification for war on Iraq.
There was "an urgent unanswerable case" for the government to instigate an independent judicial inquiry into the justification for war, he said.
It was needed to restore confidence in the prime minister, foreign secretary and in Mr Blair's ability to talk about intelligence.
It could be asked to report within six months, to call witnesses to be examined on oath and to compel the production of documents, he said.
"The only thing that remains clear about the government's position on weapons of mass destruction is it is now totally confused," said Mr Ancram.
Foreign Secretary Jack Straw accused Mr Ancram of "insulting" the intelligence committee, which would be able to see vital intelligence material for its inquiry.
A judicial inquiry could never be completed within six months, said Mr Straw.
"It would be kicked into the long grass for the next couple of years" - at a cost of up to £30m, he argued.
Instead the intelligence committee would be "rigorous and scrupulous" and deliver its findings before public interest in the issues waned.
David Kelly says he wanted Gilligan's views on Iraq
Lib Dem foreign affairs spokesman Menzies Campbell said the key question was whether the UK went to war on a "flawed perspective".
That could depend on the intelligence itself or the way it was handled once it reached the government.
It was a question "not just of truth but of judgement and competence", he told MPs.
The debate comes as members of the foreign affairs select committee ask for more evidence from Andrew Gilligan, the BBC journalist whose report sparked the row between the government and the corporation.
Mr Gilligan, who has already been questioned by the MPs in a public session, says he will reply on Wednesday to the foreign affairs committee invitation to meet him privately.
The official named by the government as his possible "mole", David Kelly, told the MPs on Tuesday he did not think he was the source of the claim that Downing Street had essentially exaggerated the threat from Saddam Hussein.
Committee chairman Donald Anderson has written to Mr Straw saying the MPs think it is "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 rejected by the Ministry of Defence.
The BBC has said it will not disclose the identity of journalists' sources.
The claims and counter-claims over the justification for war and the absence of weapons of mass destruction will form the back drop to Mr Blair's visit to Washington on Thursday.
The UK and US are already at loggerheads over allegations made by the British government that Saddam Hussein was trying to buy uranium from Niger.
The Foriegn affairs committee last week reported that the "jury is still out" on the case for war in Iraq - but cleared Downing Street director of communications Alastair Campbell of "sexing up" the dossier.