Labour leader Ed Miliband said the Prime Minister seemed to have "torn up" controversial plans for halving jail time for serious criminals in the face of a major backlash.
He also dismissed concessions over the coalition's health service shake-up that were announced yesterday, insisting Mr Cameron was "completely shameless and will say anything".
But the Premier retorted that Mr Miliband was merely "jumping on bandwagons" and displaying "weak leadership". And he backed Justice Secretary Ken Clarke, who personally championed the sentencing reforms, saying he was doing a "superb job".
The clashes came during a bad-tempered Prime Minister's Questions session in the Commons, which saw the Speaker call for language to be toned down.
Mr Cameron is believed to have ordered Mr Clarke to think again at a one-on-one meeting yesterday to discuss the plans, which are currently out for consultation.
The Prime Minister is now expected to set out the Government's final policy in a major speech on law and order later this month.
The U-turn has been greeted with delight by the Tory right - but it will leave Mr Clarke having to find up to £130 million of savings elsewhere at his department.
The Treasury has insisted there is no chance of reopening negotiations over the Ministry of Justice budget.
Raising the issue in the Commons, Mr Miliband said: "He knows and the whole country knows he is in a total mess on his sentencing policy, just like on all his other crime policies."
But Mr Cameron insisted: "What we want is tough sentences for serious offenders.
"We produced a consultation paper that had widespread support for many of the proposals that it made and in the coming weeks we will be publishing our legislation."
The Labour leader pointed out that it was the second time in two days that Mr Cameron had stepped in to execute a policy climbdown, after he announced significant changes to NHS reforms.
Mr Miliband accused the Prime Minister of breaking pledges, including that he would not introduce a "top down reorganisation" of the health service.
"I'll tell him why he made promises that he then broke. Because he is completely shameless and he will say anything," Mr Miliband said. "However much he says he loves the NHS, however many times he says it, the truth is he has got the wrong values.
"He wanted to put a free market free for all at the centre of our service.
"Any changes made now are not because he wants to make them, but because he has been found out."
Mr Cameron attempted to turn the tables on Labour by saying it had not promised to increase NHS spending in real terms.
"The reason we are able to improve the NHS is not only are we committed to reform, we are committed to more funding. The Labour Party is in favour of cutting the funding to the NHS," he said.
"What we have heard today is just a series of bandwagons... What we are seeing today is simply empty opposition and weak leadership."
As the exchanges become more heated, Mr Cameron was rebuked by Speaker John Bercow after suggesting that his counterpart had misled MPs.
"Median waiting times are down," Mr Cameron said. "That's what's happening in the NHS, that is something he misled the House of Commons about a fortnight ago."
Mr Bercow intervened: "I think the Prime Minister will be a follower of parliamentary protocol and will not suggest that the Leader of the Opposition misled the House, and I am sure that he will withdraw that remark."
Mr Cameron said: "I meant of course he gave an interesting use of facts in terms of waiting times, which are down in the NHS."
But a visibly angry Mr Miliband responded: "I think the whole House would notice he did not withdraw that."
Tory backbenchers, who have been openly hostile to Mr Clarke's proposals for increasing maximum sentence discounts from a third to 50%, were quick to seize on his discomfort.
Philip Hollobone asked the premier why, when magistrates had to retire aged 70, the justice secretary was still in his post at nearly 71.
As Mr Clarke shifted in his seat nearby, Mr Cameron replied: "He is doing a superb job and there is plenty more fuel in the tank."
Another critic, Shipley MP Philip Davies, said the Justice Secretary had been wrecking the Tories' reputation as tough on crime.
"I hope that the Prime Minister has seen that this was doing massive damage to the government, to the Conservative brand," he told Sky News' Boulton & Co programme.
"Ken Clarke was in danger of single handedly ruining the Conservative Party's reputation as the party of law and order."
Treasury minister Justine Greening said the spending settlement for the Ministry of Justice (MoJ) would not be reopened to cover the estimated £130 million cost of dropping the 50% discount proposal.
"We won't be opening up the spending review settlement that the Ministry of Justice got, but over the coming four years there will be many, many policies within the MoJ remit," she told BBC Radio 4's World At One.
"There are bound to be things that come in and go out of what they plan to spend their resources on. The MoJ has a wide-ranging budget to cover the remit it is responsible for."
Comments