Gordon Brown has said he wants to move "quickly" to reform party funding, as he attempts to reduce the furore over disguised donations to Labour.
Mr Brown said he was "angry" about the Labour donations row
The prime minister called for all-party support, saying he was "angry" about the £663,975 given by businessman David Abrahams to Labour through proxies.
He told a Newspaper Society lunch he also wanted to make the political levy paid by trade unions "transparent".
The Tories said progress would stall if Labour buried its "head in the sand".
Mr Abrahams, a property developer, gave money to Labour under four other people's names over the course of four years.
The police are investigating the donations, at the request of the Electoral Commission.
Mr Brown told the lunch at Westminster: "There will be legislation quickly on this. I hope all parties will support this legislation.
"I have told the trade unions we have to make changes to the political levy so that is transparent as well. I'm prepared to move forward with this legislation."
Mr Brown said of the donations row: "It's unacceptable. I'm angry about it, but we have got to deal with it."
He added that he was not proposing further public funding for political parties "at this stage"
Earlier, Mr Cameron repeated his offer to rejoin cross-party talks on party funding, as long as Labour tackled the issue of trade union donations.
He warned that Labour must not "bury its head in the sand" and seek to exclude unions from any cap on single donations.
He went on: "It's saddening and makes me angry that these things have happened but I think it's important when a problem emerges that you take action to deal with it."
Mr Cameron said there should be a limit on donations of £50,000 to parties, whether from an individual, a business or a trade union.
He also suggested a lower limit on general election spending, down from the current £20m to perhaps £15m.
At the weekend, Mr Brown proposed changes to party funding which hinted that trade union donations could be part of a new deal.
Mr Cameron said: "If there's a genuine change of heart in the Labour Party, of course we would be delighted to talk to them.
"But we absolutely have to know that the trades unions will be addressed. The £50,000 cap has to be applied across the board.
"Individuals have to have a real choice as to whether they pay the political levy and individuals have got to have a real choice as to which party they give the money to."
Justice Secretary Jack Straw, who had been in charge of previously failed cross-party talks on funding, will make a fresh effort to reach consensus.
Lib Dem justice spokesman David Heath said: "It's very good news if the Conservatives are genuinely prepared to rejoin all-party talks on party funding, but only if they are prepared to take matters forward rather than returning to square one."
Meanwhile, questions have been raised over the granting of planning permission to a firm, controlled by Mr Abrahams, for a business park off the A1(M) in County Durham.
Lib Dem leadership contender Chris Huhne has urged Durham Constabulary to investigate whether Mr Abrahams had gained any improper advantage in local planning decisions because of his secret donations to the Labour Party.
Mr Huhne spoke to Durham Constabulary's head of CID, Detective Chief Superintendent Ian Scott, after his complaint was passed on by Metropolitan Police chief Sir Ian Blair.
The MP told the BBC: "We had a very good and thorough conversation in which I spelled out my concerns that British politics should be not just clean but seen to be clean."
In a separate development, Work and Pensions Secretary Peter Hain has said that further donations to his deputy leadership campaign were not declared "as they should have been" to the Electoral Commission. They are not believed to have been from Mr Abrahams.