Senior European Union officials want Peter Mandelson to make a full disclosure about his relationship with Oleg Deripaska, The Times has learnt.

Lord Mandelson’s erstwhile colleagues in Brussels are increasingly concerned that the reputation of the European Commission's trade department is being dragged through the mire by continued allegations over his relationship with the oligarch.

The peer, who was forced last week to admit that the public had been misled about when he first met Mr Deripaska, continues to stonewall questions about their meetings.

There was disquiet in Europe yesterday as Lord Mandelson gave his most emphatic denial so far that he had ever done any favours for Mr Deripaska. “A lot has been said about the relationship I have with one particular Russian businessman. All I would say about that is that he has never asked for any favours, I have never given him any favours and that is what the European Commission in their examination of the issue has very firmly put on record,” the Business Secretary said as he left his London home for a four-day visit to Moscow.

He later told the Financial Times that he would not be deterred by the “sensationalist coverage of the British press” from meeting Mr Deripaska in the future.

He added that his meetings with senior business leaders as EU Trade Commissioner and now as Gordon Brown’s Business Secretary were in contrast to “George Osborne, who saw his job to secure a financial contribution to the Conservative Party through his contact with Deripaska. That’s the difference between us.”

Mr Brown tried to draw a line under the Deripaska affair, yesterday saying that Lord Mandelson’s actions as EU Trade Commissioner had all been “above board”.

“When these things are investigated by the authorities, and the authorities say there is nothing to look at, nothing causing a problem, then unless people have any other evidence it should be left,” he said.

Concern about the impact of Lord Mandelson’s refusal to give a full breakdown of his activities surfaced in Brussels during a top-level conversation late last week, according to EU sources.

José Manuel Barroso, the President of the Commission, who has been in China for several days, is expected to face demands that he should act to protect the trade department’s reputation.

Officials do not believe that they have the power to force Lord Mandelson to list his personal or professional engagements. Despite a much vaunted commitment to openness, the Commission said that Lord Mandelson’s diary is not a public document but a management tool and is therefore exempt from freedom of information rules.

There has been further criticism of his time as trade commissioner from the campaign group Corporate Europe Observatory. It has complained to Mr Barroso that the lobby group Bus-iness-Europe is too close to officials and has helped to draft EU directives.

In Britain, pressure on Lord Mandelson to detail his meetings with Mr Deripaska has continued to gather pace. William Hague, the Shadow Foreign Secretary, said: “We, and I think the whole country, do want to know transparently about the meetings that have happened and what was discussed at them and whether they ever discussed aluminium tariffs and so on.

“George Osborne has been absolutely right to set out all his contacts with Mr Deripaska, what happened at them and what they discussed. Alan Duncan, the Shadow Business Secretary, said that Lord Mandelson ought to put on record all his “interests and associations while an EU commissioner”. In fact, Lord Mandelson must file by next week his entry in the House of Lords Register of Interests. Additional information will be published in the first report by Sir Philip Mawer, the standards watchdog appointed last year by Mr Brown.

Standards of transparency are more exacting in Westminster than in Brussels. The Commission’s register of gifts records that Mr Mandelson, as he was, received four presents worth more than ¤150 (£120) between January last year and April this year, but not their value or the donor who gave him a pen, a carpet, a glass lamp and a gold-inlaid plate.

Lord Mandelson’s arrival in Russia also coincides with a crucial week for Mr Deripaska’s business interests. The oligarch is said to be scrambling to find $2 billion (£1.23 billion) to save his 25 per cent stake in Norilsk Nickel by the end of next week.

Mr Deripaska must repay part of a $4.5 billion loan for the purchase from a group of Western banks, including the Royal Bank of Scotland. He and other oligarchs have had to go cap-in-hand to the Kremlin for bailouts to save their businesses. Russia has a $210 billion rescue package to help local banks and companies and oligarchs have been queueing up.

The questions hanging over Lord Mandelson could also have a harmful effect on the first signs of improvement in Anglo-Russian relations since the fatal poisoning of Alexander Litvinenko and Britain’s decision to grant asylum to Boris Berezovsky.

A new British ambassador, Anne Pringle, has taken over from Tony Brenton, who faced the full brunt of Kremlin displeasure. The British Council won a court case over back taxes this month and Lord Mandelson’s visit will be much more high-profile than might be expected.

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