The Queen K is magnificent: 70 metres of gleaming superyacht with an entire deck for the owner and eight guest cabins below. Tempting, in short, for anyone invited on board. But Lord Mandelson should have declined. He appears to have spent at least one night on the Queen K when she was anchored off Corfu two months ago. The yacht is owned by Oleg Deripaska, Russia's “aluminium king” and, until recently at least, that country's richest man. Lord Mandelson was EU Trade Commissioner, concerned with, among other things, European aluminium tariffs.

Lord Mandelson admits knowing Mr Deripaska. But he insists this did not present him with a conflict of interests because they never discussed trade, tariffs or aluminium. He says he is “entirely satisfied that he has separated his private and public lives”, and that he sees no “legitimate public interest” in his use of his private time.

But that is for the public to decide. And when the EU Trade Commissioner enjoys the hospitality of someone in a position to benefit, however serendipitously, from his work in Brussels, the public's interest is legitimate.

Lord Mandelson should not have been a guest on the Queen K. That is why, when asked about the episode, he owed the public an honest explanation. Instead he has compounded his well-known love of the high life with his well-remembered tendency to dissemble: when asked last week whether he had stayed on the Queen K his spokesman said he had had drinks on it. Pressed further, he said that he had only met the magnate in Corfu because of a party being held there. Can he now give a straight answer to a straight question: did he stay on Mr Deripaska's vessel?