Every Labour and Conservative candidate should be held to account by voters over the Iraq war, Liberal Democrat leader Charles Kennedy has argued.
The Lib Dems want UK troops to leave Iraq by the end of the year
Mr Kennedy said Tony Blair had taken the UK into an illegal war and voters could deliver "justice by the ballot box" at the general election.
Tory leader Michael Howard says the war was right but Mr Blair lied about it.
Mr Blair says he was given clear advice the war was lawful and argues he is not asking voters to endorse his decision.
The prime minister also called for a halt to attacks on his integrity.
With 10 days to polling day, Labour focused on its efforts to regenerate cities. The Conservatives have published their manifesto for businesses.
The Lib Dems were alone among the three main parties in opposing the war, and on Sunday Mr Kennedy said the election could be a "referendum" on it.
The party took advertisements in Monday's Daily Mail and Daily Mirror newspapers underlining its opposition to the stance of Mr Blair and US President George W Bush.
The adverts show a smiling picture of the two leaders with the slogan "We oppose: Bush and Blair on Iraq. We propose: never again."
Mr Kennedy said foreign policy was not usually a major theme of British elections, but would be this time after Mr Blair misled people over the war.
He said: "Iraq does deserve to be a central issue in this election, not only because of what has happened, but because of what may yet come to pass.
"Every Labour candidate should answer for the government's rush to war. Every Conservative candidate should answer for their party's supine support."
Asked whether he would have left Saddam Hussein in power, Mr Kennedy said weapons inspectors should have had more time in Iraq.
Mr Kennedy again demanded an inquiry into "how and why" the UK went to war in Iraq, including examining ministers' judgements.
He also urged the prime minister to rule out future military action against Iran.
The Lib Dems and Tories are pressing ministers to publish Attorney General Lord Goldsmith's advice on the legality of the war.
The Mail on Sunday said a leaked memo showed Lord Goldsmith had given six reasons why military action might not be legal.
Lord Goldsmith has insisted he advised military action was lawful with his spokeswoman saying it was "his own genuinely held independent view".
Foreign Secretary Jack Straw refused to confirm or deny the newspaper report.
He was challenged on BBC Radio 4's Today programme over why Mr Blair had not seen advice from Foreign Office lawyers who thought the invasion was illegal without new UN backing.
He replied: "The fact that there was a disagreement amongst lawyers - internationally and nationally - was extremely well known."
Pressed over Lord Goldsmith's advice, Mr Blair said. "It's not a question of changing his mind. The advice of the attorney general was very clear."
He denied Downing Street had pressured Lord Goldsmith, saying: "You can go on forever trying to prove there was some conspiracy: there was not.
"There was a judgement. The judgement might be right, it might be wrong. I had to take it. I believe I made the right judgment, I believe the world is better with Saddam in prison and out of power."
Mr Blair urged people to listen to Iraqis who now saw hope for their country's future.
He accused his opponents of focusing on the issue because they had nothing to say about Britain's future.
Mr Howard accused Mr Blair of lying but said removing Saddam Hussein had been the "right thing to do".
He told Sky News' The Boulton Factor that the government's "dodgy dossier" on Iraq and Mr Blair's later characterisation of intelligence was lying.
He said the intelligence had been described as "extensive, detailed and authoritative" when it was in fact "sporadic, limited and patchy".
But he told Sky News the war had "probably" been legal, although he would have had a Cabinet meeting on the attorney general's full, written opinion.