Russia’s richest man entertained George Osborne and David Cameron’s chief fundraiser on his yacht in Corfu, leading to discussion of a £50,000 donation to the Conservative Party.

After the furore of Lord Mandelson’s stay on the same yacht, friends of the new Business Secretary have let it be known that he was not the only senior politician to enjoy the hospitality of Oleg Deripaska this summer.

In a letter to The Times, Nathaniel Rothschild, a mutual friend of Lord Mandelson and Mr Osborne, said that the Shadow Chancellor and Andrew Feldman, chief executive of the Tory party, spent time on the Queen K.

The allegations made by Mr Rothschild sparked a furious exchange of claim and counterclaim.

Mr Rothschild said that Mr Osborne and Mr Feldman discussed a donation from Mr Deripaska for Tory coffers. He also said that Mr Feldman suggested that Mr Deripaska might channel the money through one of his British companies.

The claim was vehemently denied by the Tories, who said it was Mr Deripaska who, at a later date, offered money. The Conservatives say they did not take up his offer. Donations by overseas residents are illegal, as is using a British company as a proxy to disguise an impermissible donation, under legislation passed in 2000.

Mr Rothschild’s intervention is the latest extraordinary twist in the row over the Russian billionaire, which until today centred on his links with Lord Mandelson. It is also the latest in a series of hotly contested holiday tales that have placed the Greek island at the centre of Westminster politics.

In his letter to The Times, Mr Rothschild alleges that Mr Osborne and Mr Feldman went on board Mr Deripaska’s yacht “to solicit a donation”. The claim is all the more sensational because Mr Rothschild has been involved in fundraising for Mr Cameron’s Tories and has been a close friend of Mr Osborne since they were at Oxford together.

A Conservative Party spokesman said: “The allegations made in Mr Rothschild’s letter are completely untrue. Both Andrew Feldman and George Osborne deny absolutely that they attempted to solicit a donation from Oleg Deripaska. Nor did they suggest a method by which he could conceal a donation via a British company.

“They spent a short period of time on Mr Deripaska’s boat at the invitation of Mr Rothschild. Donations to the Conservative Party were not discussed with Mr Deripaska.”

However, the Tory party confirmed that Mr Rothschild told Mr Feldman in September that Mr Deripaska wanted to make a donation to the party through his British company, Leyland Daf. A spokesman said that the offer was not taken up.

It is understood that Lord Mandelson was told yesterday of Mr Rothschild’s intention to send a letter to The Times.

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