Ed Miliband accused David Cameron of being "dodgy" as the party leaders traded blows at Prime Minister's Questions (PMQs) over the HSBC tax avoidance scandal.
The heated exchange came after reports alleged that a Swiss banking arm of HSBC advised British clients on how to dodge tax.
Miliband claimed seven Tory donors revealed in the leaked files have given nearly £5m ($7.6m, €6.7m) to the Conservative Party.
The Labour leader also alleged there was a "revolving door" between Tory headquarters and the Swiss branch of HSBC.
But Cameron hit back at Miliband and claimed no government had been tougher than his on tax evasion.
"Well, I saw this list just before coming to PMQs and one of the people named is the Labour donor Lord Paul, who funded Gordon Brown's election campaign," he said.
"I'll be very clear: people should pay their taxes in this country and no government has been tougher than this one in chasing down tax evasion and tax avoidance."
However, Miliband said the difference between him and Cameron was none of the donors had "given a penny" to Labour on his watch.
"None of these people have given a penny on my watch and he's up to his neck in this. Let's take Stanley Think, who gave £3m to the Conservative Party," he said.
"He actually appointed him as Treasurer of the Tory Party and gave him a peerage for good measure. So now can he explain what steps he's going to take to find out about the tax avoidance activities of Lord Fink?"
Cameron replied: "I will tell him, Mr Speaker, about the differences between him and me. When people donate to the Conservative Party, they don't pick the candidates, they don't choose the policies and they don't elect the leader.
"When the trade unions fund the Labour Party they pay for the candidates, they pay for the policies and the only reason he's sitting there is because a bunch of trade union leaders decided that he was more left-wing than his brother."
Stephen Green dragged into the argument
Miliband continued to attack Cameron over the HSBC scandal, accusing him of being a "dodgy prime minister surrounded by dodgy donors".
"Now, he didn't just take the money, he appointed the man who was head of HSBC as a minister. Mr Speaker, it was in the public domain in September 2010 that HSBC was enabling tax avoidance on an industrial scale.
"Are we seriously expected to believe that, when he made Stephen Green a minister four months later, he had no idea about these allegations?"
Cameron replied: "I'm glad that he's bought up the issue of Stephen Green, who was a trade minister in this government.
"This is the same Stephen Green who Gordon Brown appointed as the head of his business advisory council.
"This is the same Stephen Green who Labour welcomed as a trade minister into the government. It's the same Stephen Green who the shadow business secretary, who's looking a bit coy today, invited on a trade mission as late as 2013.
"We know what happens, Mr Speaker, every week he gets more desperate – he can't talk about the economy, he can't talk about unemployment so he comes here with fiction after fiction."
The debate comes with less than 100 days to go before the general election, with Labour two points ahead of the Tories (35% vs 33%) in the opinion polls.
HMRC chief executive Lin Homer will face questions today (11 February) before the Public Accounts Committee (PAC) about the HSBC scandal.