Liberal Democrat leadership contender Chris Huhne has said there should be "tough new legal limits" on spending by political parties.
Mr Huhne said the spending "arms race" had to end
His demand follows revelations that Labour received donations worth more than £600,000 from a property developer who used four intermediaries.
Mr Huhne, the Lib Dem environment spokesman, told the BBC the "arms race" of spending by parties must end.
He was speaking ahead of the final hustings of the Lib Dem contest.
In a BBC News 24 interview where he answered questions from readers of the BBC News website, Mr Huhne said: "I think that we need tough new legal limits on spending, to end the arms race by political parties on expenditure during elections and between elections."
He added: "Let's have a system where all trade union members and company shareholders can vote for the union or the company to give a donation - and that donation is then split according to the vote."
The Liberal Democrats' 64,000 members are voting for a new leader, with Mr Huhne and home affairs spokesman Nick Clegg the only two candidates.
The race had been largely good-tempered until last week, when it was revealed that the Huhne camp had released a briefing document entitled "Calamity Clegg".
Mr Huhne said he had "made it clear" that he had not authorised the title and that the matter had been resolved.
He added that the Lib Dems had improved their opinion poll showing in the past few weeks.
Mr Huhne said: "Broadly we have had a good campaign, where we have got across the Liberal Democrat message.
"When we put these issues across, people warm to them."
The new leader is to be announced on 17 December.
Mr Clegg was invited to take part in a question-and-answer session on News 24.
He was unable to do so, but will still be giving written answers to BBC News website readers' queries.