Ed Miliband has accused David Cameron of having "something to hide" in the row over donations to the Conservative Party and access to ministers.
Responding to a statement in the House of Commons by Cabinet Office Minister Francis Maude on political party funding on 26 March 2012, the Labour leader said it should have been the prime minister rather than Mr Maude who addressed MPs.
"It shows utter contempt for this House that the prime minister can make a statement to the media...but refuses to come here to face Members of Parliament," Mr Miliband alleged.
He added: "I think we all know why - he has got something to hide."
Mr Maude hit back, saying that Labour "did nothing" to reform party funding when in power and accusing the party of blocking previous attempts at reform.
Referring to the backing of some trade unions for Ed Miliband's campaign to lead Labour, the Cabinet Office minister said: "Now they're in opposition, their donors don't just buy policy, they elect the leader."
Former Conservative Party co-treasurer Peter Cruddas has resigned after secretly filmed footage showed him apparently offering access to the prime minister for a donation of £250,000 a year.
He made the claim to Sunday Times reporters posing as potential donors.
He said £250,000 gave "premier league" access, including dinner with David Cameron and possibly the chance to influence government policy.
In the Commons, Francis Maude told MPs that the comments by Peter Cruddas were "unacceptable and wrong".
He added that talks between the three main parties on funding were due to begin shortly.
Ed Miliband said that Labour was happy to take part in talks but that they should not be a "smokescreen" for the Conservatives.
Speaker John Bercow had to intervene several times during an angry Commons session to call for calm.
David Cameron has now said he will publish details of all donors he has had dinner with in his Downing Street flat.
The prime minister said there had been four occasions in which he had invited donors to No 10 - most of whom were friends.
All private meetings that Conservative ministers have with donors will also be published on a quarterly basis.
The Conservatives have asked Lord Gold, a Tory peer and lawyer, to examine their procedures for party donations in light of Mr Cruddas's comments.
Labour has called for an independent inquiry.