An upbeat Charles Kennedy has said his party's "big idea" focuses on policies to tackle a feeling of anxiety among the British public.

But the Liberal Democrat leader said he was "slightly cautious" about politicians who claim to offer a solution to every problem.

In a question and answer session with Liberal Democrat delegates at his party conference on Monday, Kennedy said the over-arching theme for his party's policies was the "big anxiety" among the public on issues such as international terrorism, global warming or pensions.

"The big idea for us is that we've got to offer that greater degree of security to people," he said.

In relaxed and confident mood, the Lib Dem chief told his Bournemouth audience that the Iraq war had proved to voters that the Lib Dems were a party with principles.

"That has an application that goes beyond the issue itself," he said.

Continuing the attack on the prime minister that has been a theme of the conference so far, Kennedy said Tony Blair should "explain himself" and the decision to go to war.

"I don't think we've reached the resignation issue yet," he said, adding that Blair could yet find himself "immobilised" by the issue.

"I want the truth established before the British people give their verdict at the next general election."

Labour links

Kennedy also indicated that he was unlikely to form a coalition with Labour in the event of a hung parliament after the next election, which is widely tipped to come in May next year.

He said that if Labour lost its three figure majority it would have no mandate to govern.

"Are we going to turn round and say to the British people that we are going to prop up a Labour government you have effectively dismissed? I don't think so."

But he added: "History teaches that hung parliaments tend not to happen."

The Lib Dem leader also said there was a "perverse irony" that his party's dream of proportional representation for Westminster elections was more likely to be achieved the better the party did under the current electoral system.

"We're going to have to keep winning increasingly under first past the post," he told activists.

But he said the "day would come" when introducing PR for general elections would be in the interests of Labour or the Conservatives.

Lib Dem debates

With media focus on the debate within the party over whether to position itself to the left of Labour, Kennedy denied the Lib Dems were split on the issue.

He said the party should have a vigorous debate about "individual ideas", although it should be judged on its final manifesto.

"I don't want to lead a party that is brain dead," he added. "We should never be afraid of debate."