The revelations come after Tory Party co-treasurer Peter Crudas was forced to resign over the weekend following a sting by The Times in which Cruddas intimated he could provide access to the PM for £250,000.

Cameron has condemned Cruddas’ actions and the party have labelled his words as nothing more than a boast, denying that donors were given access to the PM for cash, or that donors were given an opportunity to influence government policy.

Speaking at a Sports Relief event Mr Cameron said: “What happened is completely unacceptable, this is not the way we raise money in the Conservative party. 

“It’s quite right that Peter Crudas has resigned. I’ll make sure there’s a proper party inquiry to make sure this can’t happen again. 

“We have reformed party funding. I took over a party with £28 million of debt, it’s now virtually debt free, we’ve massively broadened our donor base, we have very strict rules, we have very strict compliance. And I’m going to make sure the rules are complied with in every case.”

Ed Miliband has however suggested that an internal inquiry is not enough. The Labour leader has demanded that the Conservatives publish a list of Tory donors who have visited Downing Street or Chequers since May 2010, and how they tried to influence policy.

“This has got to be an independent investigation into what happened, what influence was sought over policy-making, whether any influence was had or access was gained to the Prime Minister and the Chancellor,” said the Labour leader.

“The independent investigation should look at what happened at the Downing Street policy unit, because apparently offers were made or cash was paid so that the people donating money would be able to have access to it.” 

The Met Police have also received a complaint about the issue and will decide whether to investigate the issue.

The incident is particularly embarrassing for Cameron, who, two years ago, said lobbying would be the next big political scandal.

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