Cameron did not dispute the donations -- from seven unnamed individuals -- and there is no suggestion the account holders did anything illegal. But the disclosure is awkward for Cameron three months before a close national election on May 7.

It allowed Labour, level with Cameron's Conservatives in many opinion polls, to press its portrayal of Cameron and his party as putting the interests of the wealthy before those of the less well-off. Cameron rejects that charge.

"How can the prime minister explain the revolving door between the Tory (Conservative) Party HQ and the Swiss branch of HSBC?" Labour leader Ed Miliband asked Cameron in parliament.

"He's a dodgy prime minister, surrounded by dodgy donors."

Cameron laughed off the broadside.

"For 13 years they sat in the Treasury, they did nothing about tax transparency, nothing about tax dodging, nothing about tax avoidance," he said of Labour.

After the leak this month of its Swiss bank's customer list, HSBC admitted failings in compliance and controls at the unit.

Cameron is also under pressure from Labour over his 2010 appointment of Stephen Green, HSBC's former executive chairman, to be a peer and a trade minister, a role he no longer fulfils.

Cameron said on Wednesday that "every proper process" was followed when he appointed Green when pressed by Miliband if he knew about the HSBC allegations when he appointed him.

Miliband, who asserted HSBC had enabled tax avoidance on "an industrial scale", focused on the party funding issue however, accusing Cameron's party of accepting donations worth nearly 5 million pounds ($7.65 million) from seven unnamed holders of HSBC Swiss accounts.

Cameron said he had seen the same list of names and that it included the name of a British peer who had donated money to the election campaign of Miliband's predecessor as Labour leader.

So far, Green, 66, has declined to comment. HSBC said it couldn't relay questions to Green, nobody at his office in the upper house of parliament answered the phone, and the Conservatives said they couldn't speak for ministers or peers.

(Additional reporting by Kylie MacLellan and Stephen Addison; Editing by Ralph Boulton)

By Andrew Osborn