Peter Mandelson is facing continued questions over why he spent New Year’s Eve on the yacht of a billionaire who is at the centre of a major EU investigation.

The European trade commissioner admitted that he was a guest at a party thrown by Paul Allen, the co-founder of Microsoft.

Conservative leaders say that Mandelson, who was twice forced to resign from the Cabinet over allegations of sleaze, should learn the lessons of the past, demanding that he should be "totally open" and branding him "naive".

Microsoft is in a legal battle with the European Commission, which last year fined the company £355m for abusing its position in the software market.