Gordon Brown has called for an immediate review of party funding as Labour reels from the week's proxy donor scandal.
The prime minister told Labour's national executive committee this morning he wanted to use the heavy attention attracted to the donations case to force through a shake-up of the current system.
He said he was "angry" and "saddened" by the disclosure that property millionaire David Abrahams had funnelled £650,000 to Labour through intermediaries in a violation of reporting requirements.
"The last week has shown the need for immediate changes in our own party. But I would also argue it has seen the need for broader change within our system of political funding.
"Because I believe it's now time to move forward, I believe our party should now discuss and agree reform on how best to make change work.
"Openness is indeed the best guide, transparency the best system, sunlight the best solution. But I am more convinced than ever that more comprehensive safeguards for public disclosure are only the first step."
Mr Brown's comments attracted criticism from the Conservative party, who accused the prime minister of using calls for reform as a "smokescreen" distracting from the proxy donor scandal.
"David Cameron wrote to him in October urging major reforms to party funding and a cap on donations, Gordon Brown refused because he didn't want to give up on the multi-million pound financing from the trade unions," shadow Cabinet member Chris Grayling said.
"His decision to pick up the issue again today must be more than an attempt to divert attention away from party problems."
Meanwhile the property millionaire at the centre of the scandal has said Labour should have done more to prevent what he believes is a simple mistake.
Writing in the Guardian newspaper today, Mr Abrahams said the donor scandal was the "product of a cock-up, not a conspiracy".
"I trusted the party to ensure that its donations were being received and spent in the manner in which they were intended, as anyone in my position would," he wrote.
"I do not want my wealth to change the way I, as a working class boy, lead my life or get in the way of my many friendships with people with a similar background to myself."
Metropolitan police officers have begun investigating Labour's finances after a recommendation from the Electoral Commission.