Lord Mandelson was accused yesterday of hiding behind the EU code of conduct to avoid admitting the full extent of his involvement with the Russian oligarch Oleg Deripaska.

The Business Secretary faced criticism for insisting that his encounters with the billionaire - including on his yacht and at his Alpine villa - were purely social and therefore had no influence on him while he was the European Trade Commissioner.

His spokesman in Brussels added that Lord Mandelson would not take the risk of publishing details of his meetings in case the list omitted a party or another event that they had both attended, which would leave him open to accusations of lying.

Politicians in Brussels called last night for the commissioners' code of conduct to be revised because, although it insists on correct behaviour in public and private, there is no need to declare any hospitality received on holiday, or on professional trips, beyond the receipt of gifts worth more than €150 (£120).

MEPs said that it was full of grey areas, with no requirement to state publicly whether flights, meals or accommodation on social trips were funded by those seeking to influence commissioners.

Graham Watson, leader of the Alliance of Liberals and Democrats in the European Parliament, said: “Peter Mandelson has been wrong because the code of conduct is intended to apply to private and public life.

“But the code clearly needs tightening because Peter Mandelson can argue that, because he was on holiday, it does not count. We will press to have it tightened to clear up any future grey areas.”

The European Commission said that it was powerless to force Lord Mandelson to list the times and places of his social meetings with Mr Deripaska, who made his fortune from producing aluminium in post-communist Russia. Its spokesman also said that it had no plans to review the code of conduct.

“It is for Mr Mandelson to decide if he wishes to provide a list of his social engagements,” the spokesman said. “We are not aware of any circumstances suggesting any breach of rules or any conflict of interest. No evidence for such claims has been brought forward. The Commission considers that there are no grounds for an investigation.”

Lord Mandelson's spokesman at first said that he did not meet Mr Deripaska until 2006, but was then corrected by the peer, who admitted to the first meeting in 2004 in a letter to The Times. Despite a growing clamour for greater transparency from Lord Mandelson, his spokesman suggested yesterday that it was impossible to set out a definitive list of contacts.

“It is entirely normal that a commissioner should seek contact with important businesspeople in any country he or she visits,” he said. “Mr Mandelson draws a distinction between meetings he has had in his private time and in his public duty. He maintains that these meetings were in private time and as such remain private.

“What is an obvious risk is that if you have a one-to-one meeting you can probably remember that, but what happens if you have gone to a cocktail reception and a journalist sees you but you cannot recall that? So it is a very risky business to go down that line.”

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