Francis Maude, the minister in charge of transparency in government, has been accused of hiding more than £3,000 worth of hospitality he received from Richard Branson's Virgin Media.
The Cabinet Office minister, whose "jerry can" gaffe last month contributed to the Government's "omnishambles", was a guest of the telecommunications giant at the British Grand Prix at Silverstone last July.
Mr Maude is also responsible for the coalition's digital policy, raising questions over whether there is a conflict of interest. And the minister, in an article for his website as MP for Horsham, last month praised Virgin Media for "inspiring" the Government to launch a mentoring scheme.
Although Mr Maude's perk is declared on the Cabinet Office website, in accordance with the ministerial code, he has failed to record it on the Register of Members' Interests. The parliamentary rulebook states that "Ministers of the Crown who are Members of the House of Commons are subject to the rules of registration and declaration in the same way as all other members".
Last night the Cabinet Office insisted the minister had done nothing wrong. A spokesman said: "This Government is making information on hospitality available to the public that they were never able to access in the past, and will continue to do so. Any hospitality that is received as a minister has to be recorded in the ministerial list – and that is exactly what has happened here."
Asked whether the failure to declare the perk was consistent with Mr Maude's role, an aide said: "He takes transparency issues extremely seriously and is trying to make sure this Government is a world leader in transparency."
But the shadow Cabinet Office minister, Michael Dugher, said: "Francis Maude has very serious questions to answer as to whether he broke parliamentary rules.
"He cannot seriously say that his ministerial responsibilities have got anything to do with attending the Grand Prix with this company. So it looks like he has tried to pull a fast one by burying the fact that he attended the event with a cursory reference on the Cabinet Office website and by not declaring it with all the proper details in the Register of Members' Financial Interests.
"Francis Maude is always lecturing people about maximum transparency. He should practise what he preaches and come clean about this."