LONDON (Reuters) - Publication of a secret 2003 memo from the government's top lawyer questioning the Iraq war's legality buffeted Prime Minister Tony Blair on Thursday, just a week before the May 5 election.
Trailing in opinion polls, opposition parties pounced on the report from Attorney General Lord Peter Goldsmith as showing Blair had deceived Britain.
"If you can't trust Mr Blair on the decision to take the country to war -- the most important decision a prime minister can take -- how can you trust Mr Blair on anything else ever again," asked Conservative leader Michael Howard.
Blair, confident Labour's strong economic record will win him a third term, called the affair "a damp squib".
Having refused past demands to release the memo, Blair authorised full publication on Thursday to try and defuse the row after excerpts were leaked to media.
The deeply unpopular Iraq war remains Blair's Achilles Heel, enabling foes to attack him on trust and integrity.
Thursday's cacophony of claims that Blair leant on Goldsmith to swallow his doubts echoed accusations the government also pressured intelligence services to hype evidence of Saddam Hussein's banned arms before the 2003 U.S.-led invasion.
The Goldsmith leak has ruined Blair's efforts to focus the campaign run-in on domestic issues like the economy and health.
But analysts said it was unlikely to sway many voters at this late stage. "They don't trust Mr Blair to tell the truth, but they have long ago made up their minds about that and there is no reason to think that they would trust the Conservatives any more," political analyst Anthony King told Reuters.
The March 7, 2003 document creating all the furore shows that Goldsmith cast doubt on the legal grounds of war just days before Blair ordered troops in.
Goldsmith said then "a court might well conclude" U.N. Security Council resolutions at the time did not authorise war and that "the safest legal course" was a fresh U.N. motion.
But he was not categorical, also saying Britain could build "a reasonable case" for war based on two earlier U.N. resolutions if it had "hard evidence" of wrongdoing by Saddam.
Ten days later, when Britain had failed to get a new resolution, Goldsmith gave the cabinet and parliament short written advice that war was legal -- and mentioned no doubts.
SMOKING GUN OR DAMP SQUIB?
Blair, President George W. Bush's closest foreign ally, denied Goldsmith bowed under political pressure.
Looking frustrated at times at a news conference intended to trumpet Labour's business policies, Blair said Goldsmith's conclusion was unequivocal and that he had expressed his full thoughts in person at a Cabinet meeting.
"Contrary to the stuff in the papers, he did advise that it was lawful to proceed on March 7 and March 17 ... This so-called smoking gun has turned out to be a damp squib," he said.
"People can carry on trying to frame this in terms of my integrity, but it was about a decision. I took it. I have to live with the consequences of it ... It was better for this country's security and the security of the world to remove Saddam and put him in prison rather than have him in power."
Chancellor Gordon Brown -- widely viewed as Blair's rival for power and probable successor -- jumped to his boss's defence in another show of unity between the pair that has served Labour well in the campaign.
"This was the most difficult decision a Cabinet can make but the decision was made in an honest, principled and clear way with the evidence before them," he said, next to Blair.
The media, however, leapt gleefully on the biggest story so far in an otherwise lacklustre election campaign.
"Blair Lied and Lied Again", the right-wing Daily Mail said.
Iraq, though, has yet to register significantly in opinion polls, which show electors more bothered with domestic issues.
Two new surveys on Thursday put Labour on 40 percent and the Conservatives on 33 and 31 percent respectively.