Chris Huhne said Labour could not win the next general election
The Lib Dem home affairs spokesman has accused David Cameron of talking "touchy feely, policy free waffle".
Chris Huhne also said Shadow Chancellor George Osborne "had never done a proper job in the real world" and lacked the experience to fix Britain's economy.
He said the "game was up" for Gordon Brown, but added: "Just because Labour cannot win doesn't mean the Tories have to win."
"We hold the torch of progress now," Mr Huhne added.
Speaking at his party's conference in Bournemouth on Tuesday, Mr Huhne said Britain needed "a new system of politics".
He said Labour could not win the next general election, but insisted the Tories were not the ones offering the right kind of change.
"Cameron's key message is 'I am not Gordon Brown'. It's empty. It's negative, and it won't stand up to the scrutiny of a campaign," he said.
Mr Huhne compared the shadow chancellor unfavourably to the Lib Dems' own Treasury spokesman Vince Cable.
"George Osborne may have been well educated, but he has never done a proper job in the real world in his whole life," he said. "Never hired. Or fired. Never had to meet a budget or a payroll. Never taken tough decisions.
"It's not his fault, but he just hasn't got the experience. Britain in recession can't risk a chancellor learning on the job."
'Wackos and weirdos'
Mr Huhne warned that "a vote for the Tories is a vote for more crime" and said that if the Conservatives repeated their past record there would soon be a million more crimes each year.
He also said the Lib Dems were leading the way on safeguarding civil liberties, with plans to pass a Freedom Bill which would scrap existing policies like identity cards.
"If the Conservatives are really against the surveillance state, why do they promise to remove the current checks on police surveillance?
"If the Tories believe that we are innocent until proved guilty, why do they refuse to vote against control orders? If they are really for human rights, why would they ditch the Human Rights Act?
"I don't want second-class Tory justice. I want first-class fairness."
Mr Huhne also accused Mr Cameron of forming allegiances with "wackos and the weirdos" elsewhere in Europe.