Political parties could get access to "greater levels" of public finance, the man reviewing funding arrangements for the prime minister has suggested.
Capping donations to parties was another suggestion
Sir Hayden Phillips warns that "we cannot have a healthy democracy for nothing", in an interim report due to be published on Thursday.
His views were revealed in a press release to accompany the report, mistakenly posted online a day early.
Labour and the Conservatives have said they are in broad agreement with him.
Sir Hayden puts forward options but, it appears, will not recommend one yet.
Instead he sets out four scenarios for the future of public funding: minimal change, increased transparency, a cap on donations and greater levels of public funding.
'Party politics costs'
He said: "The point of party politics is a competition to serve the public interest."
UK politics had "historically, and in international terms, been remarkably free of corruption and abuse", the press release says.
Sir Hayden added that the way parties were funded could "diminish cynicism and restore confidence if it can play a part in encouraging better engagement between parties and voters over time".
But the public could not "have it both ways". Party politics costs, he adds.
"While parties can reduce the amount they spend, they will still need to get some money from somewhere, whether from donations or public funds, or a mixture (as now) of both."
Conservative Party chairman Francis Maude said he agreed with the "direction" of Sir Hayden's thinking
He added: "It's clear that, if public funding for political parties is to increase, political parties must tackle the perception that donations can buy influence or favours. That's why we support a cap on donations."
He said it was for Chancellor Gordon Brown to decide whether the time had come to sever financial links with the unions.
Labour chairman Hazel Blears welcomed Sir Hayden's work and said the party was "absolutely committed to increased transparency and accountability in political party funding".
She said Labour wanted a system "that is fair to all" and encourages a wider political discourse and confidence in politics.
Sir Hayden's final report is due to be published before the end of the year.