Mr Brown accused the Tories of "another U-turn on policy" and said he had set aside £670m in the next year - £420m of which would come from the NHS to provide care for urgent needs.
"Surely a party that supported the policy one week, shouldn't be opposing it the next week?" Mr Brown asked.
He said the Tories had asked for talks with Health Secretary Andy Burnham to get a consensus on the issue but had now "broken the consensus".
The Tory leader said some figures suggested the policy could put £26 on council tax and said some Labour councillors and peers were also angry about the policy.
Questions over levy
"What we want to know is where is the money coming from? People who work closely with you are completely opposed to the way this is being done," Mr Cameron said.
He said one option in the Green Paper was for a "£20,000 levy on every single elderly person in this country except the very poorest" and repeatedly urged Mr Brown to rule out a levy.
Any progress that had been made has now been undermined by this descent to a puerile level of political point scoring
Norman Lamb Liberal Democrats
Amid shouting and jeering in the Commons the prime minister said: "The wall of noise will not disguise the fact that the Conservative Party have absolutely no policy on an issue that is vital to the needs of the elderly."
Liberal Democrat health spokesman Norman Lamb said an attempt to build a consensus between the parties had been "undermined by this descent to a puerile level of point scoring".
He added: "The current system is in crisis with many elderly people getting inadequate care. The Liberal Democrats want to see a cross-party agreement on social care to sort this problem out once and for all."
The Times letter says that councils support providing extra help to those with the greatest care needs, but that the current plan risked putting strain on a system already facing tight finances.
The councils say they have "major doubts" over how the scheme would be funded and suggest expectations would be raised among many vulnerable people "when the reality may be significantly different".
Ministers say the pledge could help 400,000 people to stay in their own homes each year.
Care Services Minister Phil Hope said it was extremely disappointing that local authorities supported the principle, but were quibbling about making it happen.
The Association of Directors of Adult Social Services said it backed the idea, planned for implementation in England, but wants a rethink on the funding.
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