By Iain Watson
BBC News political correspondent
Peter Mandelson says he is getting on with his job but past questions remain
George Osborne admitted yesterday his trip to Oleg Deripaska's yacht off the Corfu coast in the summer "didn't look good".
But he is adamant that he has set out a full account of his meetings with the Russian billionaire.
The Conservatives are hoping attention will now focus on one of Mr Deripaska's other temporary shipmates, Lord Mandelson, who also visited the luxury vessel this summer.
Lord Mandelson admitted at the weekend that he first met Mr Deripaska in 2004, two years earlier than his office had previously indicated.
And he has certainly had meetings in colder climes than Corfu - a dinner in Moscow was described in detail by his former aide Benjamin Wegg Prosser in his blog recently.
So Lord Mandelson has come under pressure - most recently from the shadow foreign secretary William Hague - to list all his engagements with Mr Deripaska during his four years as the EU's trade commissioner.
Business versus pleasure
So far he has resisted, but the key question appears to be: did Peter Mandelson mix business with pleasure?
In a rather tetchy briefing in Brussels yesterday, a European Commission spokesman said "it is for Mr Mandelson to decide if he wishes to provide the list of his social engagements, and I underline social".
In other words, nothing to do with them, guv.
At the same briefing, the spokesman for the current trade commissioner - who was also Peter Mandelson's spokesman when he was trade commissioner - said "Mr Mandelson draws a distinction between meetings he's had in his private time and in his public duty".
He added: "He maintains these meetings were in private times, and as such remain private."
But Lord Mandelson's critics say that he, himself, has undermined this defence in an interview with the Financial Times.
He said "my job as trade commissioner is to make contacts with senior economic and business leaders in economies like Russia's. ...This is in contrast to ...George Osborne who saw his job to secure a financial contribution to the Conservative party though his contact with Deripaska. That's the difference between us."
Of course George Osborne denies asking for a donation, but these comments raise the question of whether Lord Mandelson was acting as a guest or as trade commissioner - or both - aboard Mr Deripaska's yacht.
If this was semi-official business then should he provide more detail of this and other meetings with Mr Deripaska?
Actually, the European Commission has another line of defence to prevent full disclosure of Lord Mandelson's meetings with the Russian billionaire.
While Commission documents are subject to freedom of information provisions, they say that Lord Mandelson's diary isn't a "document" and is exempt from publication.
Something to declare?
So enter the Lib Dems - none of whom, as far as we know, were aboard the Deripaska yacht this summer.
The leader of the Liberal and Democrat group in the European Parliament, the British MEP Graham Watson, says it is the Commission that may have questions to answer.
He wants the code of conduct governing European commissioners tightened up.
He believes Lord Mandelson should not "hide behind an excuse of being on holiday" and should have declared any hospitality he received from Mr Deripaska.
He wants any "grey areas" in the code of conduct transformed into black and white rules so that "any hospitality received by a Commissioner in his or her private life should be declared in the same way as in his or her public life".
The Commission, however, says it has no plans to change its rules and insists there is no evidence of a conflict of interest in Lord Mandelson's meetings with Mr Deripaska while trade commissioner.
But, as was shown by the questions put to Lord Mandelson by reporters during his current trip to Moscow, that position has failed to put an end to the affair.