Dr Fox and Adam Werritty were among a noisy group who downed eight bottles of bubbly on the Commons terrace, with at least one cork being popped into the River Thames. The event took place within an hour of Dr Fox, 54, being given a key Brexit role in Theresa May’s new Cabinet. His friends queued up to give him congratulatory slaps on the back as he drank £29-a-bottle House of Commons champagne.

The impromptu party, hosted by Commons Deputy Speaker and fellow Tory MP Eleanor Laing, a longstanding friend of Dr Fox and his wife Jesme, was attended by about 20 people. They got through eight bottles over a couple of hours. Mrs Fox was not present.

Dr Fox was forced to resign as Defence Secretary in October 2011 in a row over his dealings with Mr Werritty. The lobbyist did not have security clearance but accompanied Dr Fox on at least 18 foreign business trips.

The resignation came after a week of revelations about Dr Fox’s relationship with Werritty, including disclosures that the friend’s activities were funded by firms and individuals that potentially stood to benefit from government decisions.

At the time, Werritty falsely described himself as one of Dr Fox’s official aides and handed out business cards bearing the Commons portcullis logo. He also took a number of solo trips reportedly with the aim of fostering closer ties between Right-wing politicians in Britain and the United States.

In his resignation letter to the then Prime Minister David Cameron, Dr Fox said he had ‘mistakenly allowed the distinction between my personal interest and my Government activities to become blurred’.

Mr Werritty, 37, best man at Dr Fox’s 2005 wedding, moved into Dr Fox’s spare room in London after graduating from university. Werritty now lives in a flat in Dolphin Square, Pimlico – a mile from the Commons – where many MPs have apartments.

An inquiry cleared Dr Fox of benefiting financially from his links with Werritty.

An MP who saw Dr Fox’s champagne party said: ‘It seemed a bit over the top to celebrate so loudly in full view of members of the public on Westminster Bridge.’

Dr Fox said last night: ‘Adam and his wife were invited by Eleanor.’ He added: ‘My friends are my friends and I’m very loyal to them.’