Conservative leadership rivals David Davis and David Cameron have accused each other of opportunism.
Tory MPs must not vote with "dinosaur" Labour MPs against public service reforms which make sense, Mr Cameron warned during a televised debate.
Mr Davis, meanwhile, said his rival's "u-turns" on health, immigration and education smacked of inconsistency.
The pair were speaking in a head-to-head debate on ITV1's Jonathan Dimbleby programme.
The pair clashed on drugs policy, tax and licensing reform but the question of tactics paved the way for the most heated exchanges.
Shadow education secretary Mr Cameron said the party should not be afraid to support Prime Minister Tony Blair over issues it agreed with.
Mr Cameron, 39, said: "The alternatives are either back them and say yes let's improve it further.
"Or go through the divisions lobbies in the House of Commons with Frank and Jeremy Corbyn and people who, frankly, if you put them in the Natural History Museum the dinosaurs would walk out in objection."
That would be "too opportunistic", he argued.
Mr Davis, on the other hand has pledged not to "prop up" the prime minister.
Tory voters had been deceived by "used car salesman" Mr Blair on previous occasions, he said.
Tories initially backed reforms for licensing and the expansion of casinos only for Mr Blair to change his mind, he added.
"We don't want to be an accomplice in a confidence trick on the British public."
Accusing Mr Cameron of changing policy on health care, tuition fees and immigration "on the back of a single election loss", it was Mr Davis' turn to accuse his rival of opportunism.
"That is not consistent.
"That can easily be represented, maybe misrepresented, but it can be represented as opportunist on the back of an election result."
Mr Cameron replied: "The Conservative Party has got to look at the fact not that we lost an election but that we lost three."
The party would lose again if changes were not made, he said.
Covering familiar campaign ground, Mr Davis, 56, was accused of having a "reckless" tax policy, countering that Mr Cameron's was "vague".
The shadow home secretary says he will limit growth in government spending to 1% below the rate of economic growth.
His rival has promised to "share the proceeds" of growth between the voters and the Treasury.
Meanwhile, in a separate interview with the BBC's Politics Show, Mr Cameron said his party must do better in Scotland to help win over the "hearts and minds" of British voters.
He was speaking ahead of a Monday visit to Perth where he will go head-to-head with Mr Davis in the latest in a series of hustings.
Mr Cameron has called on Scottish Conservatives to campaign for tax cuts at Holyrood.
Conservative Party members are currently voting for who they want as the leader, with the result expected on 6 December.