Prime Minister Gordon Brown insisted Saturday there was "nothing untoward" in the dealings of a key cabinet minister with a Russian oligarch, which has sparked a political row in Britain.

Former European Union trade commissioner Peter Mandelson, now Brown's Business Secretary, said in a letter to The Times newspaper Saturday his contact with aluminium magnate Oleg Deripaska, Russia's richest man, went back to 2004 -- two years earlier than previously stated.

Mandelson's letter said the initial statement about his meetings with Deripaska went to the media while he was in hospital and stressed that he had met with "a great number of business people round the world" as Europe's trade commissioner.

"This was already investigated by the European Commission when he was a commissioner and the answer was nothing untoward happened," Brown said of Mandelson's meetings.

"That's where the story lies," Brown emphasised.

In another Times letter this week, main opposition Conservative finance spokesman George Osborne was accused by financier Nat Rothschild of having helped solicit a 50,000 pound (63,000 euro, 82,000 dollar) donation from Deripaska while staying with Rothschild in Corfu in August.

The premier has already called for a probe into Osborne's involvement.

Brown's backing comes as British media interest in the story, which involves two multimillionaires, a yacht and glitzy holidays on the Greek island of Corfu, rages on.

Osborne admits he met Deripaska five times including twice on the oligarch's yacht the Queen K in Corfu in August.

He says Rothschild suggested to Tory fundraiser Andrew Feldman that Deripaska could be interested in making a donation.

Conservative officials later decided it "would not be appropriate to accept such a donation" from Deripaska.

Osborne denies he or Feldman solicited a donation from Deripaska or suggested this could be concealed through a British company Deripaska owns.

Only individuals who appear on Britain's electoral roll or legitimate British firms can donate to political parties.