Tony Blair at a media conference in London. (Reuters)

London, April 25 (Reuters): Prime Minister Tony Blair faced demands today for a new probe into the Iraq war as his rivals launched a concerted attack on him over the US-led invasion for the first time in Britain?s election campaign.

The anti-war Liberal Democrat party placed advertisements in newspapers showing a smiling Blair beside President George W. Bush under the headline: ?Never Again? and called for a public inquiry into Blair?s decision to go to war.

?Britain?s international reputation has been damaged by the way Tony Blair took us to war,? party leader Charles Kennedy said. ?Tony Blair says history will be his judge. He is wrong. The British people will be his judge.?

Blair?s trust ratings have plunged over Iraq but his government has already survived two major public inquiries into the war and analysts said it was unlikely to agree to another.

Iraq hit the top of the election agenda over the weekend as Blair?s Conservative opponents accused him of lying.

A Sunday newspaper claimed the government?s top lawyer gave six reasons why Blair might breach international law if he went to war without a second UN resolution. The attorney general later ruled the invasion was legal, prompting opponents to claim he had been put under pressure.

Blair said no pressure had been applied but foreign secretary Jack Straw fell short of explicitly denying the report. ?I?m not confirming what is alleged to have been in a leaked document,? he told BBC Radio. ?I?m simply not confirming it.?

Conservative leader Michael Howard said Blair had overstated the ?sporadic and patchy? intelligence gathered by Britain?s intelligence services on whether Iraq had banned weapons.

The Prime Minister has repeatedly defended his decision to support Bush?s 2003 invasion of Iraq and has denied hyping the threat posed by former Iraqi President Saddam Hussein.

He said today the attorney general clearly advised the war was legal. ?There is no point going back over it again and again and again,? Blair said. ?I don?t regret the decision I took.? While Iraq has not loomed as a major electoral issue so far, Labour strategists admit its impact, particularly on public trust in Blair, remains an unknown.

Opinion polls today suggested voters view domestic issues, such as public services and the economy, as paramount.