David Cameron is under increasing pressure to reveal whether the Conservative Party's millionaire backers have been enjoying private dinners in Downing Street where they can lobby for changes to government policy.
Labour will try to force a minister to come to the Commons today to explain why the Tory co-treasurer, Peter Cruddas, was recorded boasting of the access a donor could buy for £250,000.
Mr Cruddas (below) resigned as soon as the scandal broke, and his remarks were disowned by senior Tories, who dismissed him as a newcomer to politics who did not understand the system and was making boastful promises that he would never have been allowed to fulfil.
Mr Cameron told the BBC: “What happened is completely unacceptable. This is not the way that we raise money in the Conservative Party. It shouldn't have happened. It's quite right that Peter Cruddas has resigned. I will make sure there is a proper party inquiry to make sure this can't happen again.”
But Labour politicians refused to accept that Mr Cruddas, who has himself given hundreds of thousands of pounds to the Tories, was genuinely ignorant about the relationship between political influence and party donations.
Mr Cruddas, the founder of an online trading company, Currency Management Consultants, was recorded by undercover journalists from the Sunday Times promising that a £250,000 donation would be rewarded by dinners with David Cameron and the Chancellor, George Osborne.
He claimed that some donors had dined privately in 10 Downing Street with David and Samantha Cameron, and told the journalists that issues raised by “premier league” donors would be passed on to “the policy committee”. It is assumed he was referring to the No 10 Policy Unit.
The Labour leader, Ed Miliband, claimed that the remarks raised issues too serious to be handled by an internal Tory party investigation. “There needs to be a proper independent investigation into what influence was sought, what influence was gained and what impact it had,” he said.
“I think people are bound to ask questions about whether policy is being made in the national interest or the Conservative Party's interest.”
As part of the operation to limit the damage caused by Mr Cruddas's remarks, the Conservatives said they want to reopen stalled talks on reforming the funding of political parties. All the main parties concur that the system needs reform, but they have been unable to agree the details.
Last November, the former standards watchdog, Sir Christopher Kelly, proposed a £10,000-a-year limit on donations from individuals or organisations, including trade unions. The Conservatives object that the figure is too low and should be £50,000, while the Labour Party argues that the funds it receives through trade unions are actually small donations from union members and should not be subject to the cap.
The former Liberal Democrat leader, Sir Menzies Campbell, said yesterday that the Cruddas affair had strengthened the case for the state funding of political parties, though other leading Liberal Democrats have shied away from asking for greater taxpayer subsidies in the middle of a recession.
Peter Cruddas was Tory principal treasurer for less than a month before he was forced to resign.
Mr Cruddas, who is 90th in The Sunday Times Rich List, has amassed a £750m fortune. In 2006 he was described as the richest man in the City.
The Arsenal fan, who left school aged 15, and ex-banker founded internet securities dealer CMC Markets in 1989 with a £10,000 investment.