Prime Minister Tony Blair has come under renewed pressure from his election rivals over the war in Iraq.
Mr Blair insists the Iraq war was right and legal
Tory leader Michael Howard has accused him of lying about the conflict.
Charles Kennedy says he must publish the attorney general's full legal advice on the war - after a newspaper claimed a memo raised legal concerns.
The Lib Dem leader said the election could be a "referendum" on the decision to go to war. But Mr Blair insists the conflict was right and legal.
Speaking in south London, Mr Kennedy said: "The longer he [Mr Blair] holds back from making that full disclosure, the more people are perfectly entitled... to view this general election as a referendum on his conduct and on the government's decision-making over taking us into that war."
The comments followed a report in the Mail on Sunday, which said a leaked memo showed Attorney General Lord Goldsmith had given six reasons why action might not be legal.
Lord Goldsmith has insisted he advised that military action against Iraq was lawful - with a spokeswoman saying that this was "his own genuinely held independent view".
'Sporadic and patchy'
International Development Secretary Hilary Benn, responding to the newspaper report, said he did not think "there is anything new in this at all".
"The Attorney General has been absolutely clear on a number of occasions. It was his own advice and the advice that he gave was that military action was legal."
Earlier in the week, Mr Blair defended his decision to go to war in Iraq as a tough choice but one that was "the right thing to do".
Charles Kennedy is expected to make the Iraq war a key campaign issue this week
He told BBC Newsnight's Jeremy Paxman people had to make their own judgement but he took the decision he had to.
A Labour Party spokesman said: "Michael Howard supported Britain's use of military force in removing Saddam Hussein. Now he is opportunistically trying to win the votes of those who opposed."
On Sunday, Mr Howard said Mr Blair had lied in the run-up to the Iraq war about the intelligence.
Speaking on Breakfast with Frost, Mr Howard said. "The intelligence that he had, as we know from the Butler report... was limited sporadic and patchy.
"When Mr Blair came to report that to the country, he said he had intelligence that was extensive, detailed and authoritative.
"Maybe you can reconcile those two different sets of words. I can't. I think that portraying the intelligence in that way was untrue."
Mr Kennedy, asked about Mr Howard's comments, said he would not stand for any Conservative "claptrap" about a war for which, he said, they were the chief cheerleaders.
The Liberal Democrats, who were the only one of the three main parties to oppose the war, are expected to increasingly concentrate on the issue when the last full week of the campaign gets underway on Monday.
On Sunday all three party leaders have made speeches to call for more action on world poverty to mark world poverty day.
The emergence of Iraq as an issue comes as a YouGov poll for the Sunday Times suggests Labour support is at 37%, Conservatives at 33% and Lib Dems on 23%.
An ICM poll for the Sunday Telegraph suggests Labour has 39% support, Conservatives 33% and the Lib Dems 21%.
The Sunday Times claims to have a leaked memo sent by Labour's chief election strategist Alastair Campbell saying that Mr Howard's focus on immigration was "turning off" voters in the centre ground.
The paper says the memo goes on to warn that low turnout could hit Labour "very hard", although it adds "so far we have been engaged in making and winning arguments. This job is largely done".