The Tories are finished as a "serious challenger for government", the Liberal Democrats have claimed at their party conference in Bournemouth.
Kennedy: Attacked by press
The party's campaigns chief Lord Razzall predicted that when voters finally lose faith in Labour, the Lib Dems would form the next government.
He also warned senior Tory figures his party was coming after them.
The Tories said it was "utter nonsense" for the Lib Dems to portray themselves as "political heavyweights".
Lord Razzall told Lib Dem delegates: "I am not going to make the same mistake a former Liberal Democrat leader made some 20 years ago and tell you to go back and prepare for government.
"That's not my style and it's not Charles Kennedy's style.
He said told delegates the Conservative party was "finished as a serious challenger for government in all of our adult lifetimes".
To loud cheers from delegates, he said: "There will come a moment - and that moment may be sooner than we think - when the British public finally loses faith in this Labour government."
And when that happens, he said, "the next party of government would be not be Conservative but Lib Dem with Charles Kennedy as prime minister".
Responding to the Lib Dems claim, Tory party chairman Liam Fox said: "The Conservatives are the dominant party in local government by a considerable margin.
"Charles Kennedy's foolish bravado ignores the fact that under Paddy Ashdown in 1996, the Lib Dems controlled 55 councils- this figure has now dropped to 30."
Earlier, the party agreed the policies it would campaign on at the next general election.
The party's pre-manifesto was adopted with one amendment, safeguarding a publicly funded NHS free at the point of use.
Its plans to end all university fees and bring in free personal care of the elderly was adopted.
A new 50% tax rate for all earnings above £100,000 a year would help pay for the plan.
The Lib Dems insist their plans are fully costed but Labour Chief Secretary to the Treasury Paul Boateng said their figures did not add up.
"The Lib Dem draft manifesto adds significant further costs to the 100 separate spending commitments they've made over the last two years," said Mr Boateng.
Delegates have also heard plans for "green incentives" to cut pollution.
Speaking on the BBC's Breakfast, Mr Kennedy claimed the party had both Labour and the Conservatives rattled, following attacks in the left and right-wing press.
"The Liberal Democrats are something different, the party of the future. We are going places and that is why we are under attack, but we are up for it," he said.
The conference in Bournemouth also debated the future of Iraq and a motion calling for the coalition to account fully for the expenditures of the Iraq development fund and cash gained from Iraq's oil revenues.
Defence spokesman Paul Keetch said the war would be the lasting memory of Mr Blair's tenure.
Foreign Affairs spokesman Sir Menzies Campbell told the BBC the UK should begin planning for a phased withdrawal of troops to start once a democratic government is in place in Iraq.
The party has also been debating its education policy, which not only includes scrapping tuition and top-up fees for universities but calls for increased vocational opportunities for youngsters aged over 14.
Education spokesman Phil Willis promised to limit class sizes to 20 for five to seven-year-olds and 25 for eight to 10-year-olds.
The government's limit of 30 per class did not go far enough, he said.
Delegates also heard calls from transport spokesman John Thurso for a high-speed rail link between Edinburgh and London.
The Lib Dems say work on the link, which would cost up to £12bn and take pressure off the existing network, could begin in 2013 and be completed 10 years later.