Charles Kennnedy has urged voters to make the next general election a referendum on the Iraq war.

In his closing speech to the Liberal Democrat conference, Kennedy called on the prime minister to tell MPs when he offered George Bush his support for the war on the grounds of regime change.

"It's time we got an answer. And if the prime minister still refuses, then the people can make their judgment because the ultimate verdict is the general election itself."

He suggested institutional reform was required to prevent a prime minister pursuing unilateral military action, without the support of the United Nations.

"Never again should such supreme prime ministerial power be allowed to progress without sufficient checks and balances," Kennedy told his troops.

He also attacked the Conservatives for their uncritical support of the conflict.

"Never again should a so-called official opposition be entitled to that name when it so pathetically fails to fulfil its most basic parliamentary function and duty," he said.

The Guardian says that the speech was "widely hailed as the most effective of his leadership."

However Telegraph sketchwriter Andrew Gimson says that the "speech appeared to be based on the common fallacy that to be taken seriously you have to be dull".

Writing in the Times, Peter Riddell says: "The Liberal Democrats aspire to be a party of power, not protest. Yet they still sound like a party of opposition."