Charles Kennedy has rallied Liberal Democrat election candidates in London with a call to be "proud" about tax and spending pledges.

Despite promising to fight a "positive campaign" the party leader also attacked his opponents in a speech designed to send his activists out into the country on a high note.

He launched the party's "battle bus" and campaign theme song - Jan Sibeliuson's "Karelia Suite" - on Sunday and promised to "take seats from both Labour and Conservative in each and every region and nation of the country".

Kennedy told the gathering to be upfront about Lib Dem tax and spending plans of a 50 per cent top rate of tax for the highest earners.

"We say no hidden taxes - we have one tax raising measure which will affect one per cent of taxpayers," he said.

"One new tax on one per cent of earners. And we should be proud of what that will pay for - an end to tuition fees; providing free personal care for the elderly; and reducing the burden of local taxation.

"Then we will redirect £5bn a year of existing government spending to pay for priorities like pensions and more police."

'Waste'

In a rare negative attack he accused the government of "wasting" its time in office.

"Labour has wasted the opportunity given to it by the British people over these last eight years," the third party chief said.

"Under Labour the poorest 20 per cent of people are paying more of their income in tax than the wealthiest 20 per cent.

"When you break your promises over tax increases and student top-up fees people don't forget. Nor will people forgive the fact that Tony Blair lined up with George Bush and we were misled into the Iraq war.

"People feel badly let down by Labour. They're never going to regain the trust of the British people.

"Britain is in so many ways a fortunate country - and a good country to live in. We have principles of tolerance and social justice. By international standards we are an affluent society.

"But we can and must do better. We're not in the business of talking Britain down. We're going to talk Britain up. We are ambitious for Britain." 

Opposition

Turning to the Tories, he said they had failed to provide tough scrutiny of the government.

"There have been issues in this last parliament where we Liberal Democrats have had to provide the real opposition to the Labour government; over Iraq, over top-up fees, ID cards, the council tax," Kennedy said.

"On each and every one of these issues, the Conservatives have lined up with Labour or flip-flopped on the issue under dispute.

"The Conservatives just can't offer credibly the fresh alternative that the country is looking for. They are a party of the past, not the future.

"That is why there are no limits to our ambition and there are no no-go areas for the Liberal Democrats.

"We will take seats from both Labour and Conservative in each and every region and nation of the country."