George Osborne struggled not to laugh but refused to comment on the extraordinary allegations that David Cameron "inserted a private part of his anatomy" into a dead pig's mouth during an initiation at university.
Extracts of a new biography of the Prime Minister also included claims that he smoked cannabis with friends, allowed cocaine in his London home and alleged that he misled the public over the non-dom status of Lord Ashcroft, the co-author of the inflammatory new biography Call Me Dave.
The Chancellor, asked by reporters during his trip to China what he made of the claims, simply said: "I haven't seen that book".
Lord Ashcroft and Mr Cameron fell out after the Tory leader allegedly failed to make good on a promise to give the prolific Tory donor a top job once he became Prime Minister in 2010. The new biography is seen by some as an act of revenge after years of feuding between the pair.
The book accuses David Cameron of being part of a debauched group called the Piers Gaveston Society, as well as the infamous Bullingdon Club, during his time at Oxford.
Lord Ashcroft and the book's co-author, Isabel Oakeshott, the former Sunday Times political editor, wrote that an unnamed “distinguished Oxford contemporary”, who is now an MP, recalled how Mr Cameron took part in an “outrageous” initiation ceremony at a Piers Gaveston event.
“His extraordinary suggestion is that the future PM inserted a private part of his anatomy into the animal’s mouth,” an excerpt published by the Daily Mail claimed.
Lord Ashcroft wrote that the man made the same allegation three times, with increasing detail, and claimed a photograph existed of the act.
Its alleged owner has not responded to Lord Ashcroft’s request to view the photo, and the peer wrote that it may be a “case of mistaken identity”.
Watch Mr Osborne try not to laugh when asked about the allegations in China:
The book also contains allegations that smoked cannabis with university friends who nicknamed themselves the "Flam Club", and later later allowed cocaine at his home in London.
A spokesperson for the Prime Minister told The Independent: “It’s a no comment from us. On any of it.”
Few sitting MPs have commented on the story but the Liberal Democrat leader, Tim Farron, wrote on Twitter: "I've never been more pleased to be a vegetarian."
Former Conservative MP Louise Mensch emphasised that the claims were unproven and characterised the story as: “I didn't see anything – but a mystery bloke has a photo.”
She added: “I'm sorry, Corbyn fans. Cam just didn't Kermit the Crime.”
Others suggested that the unnamed source may be trying to damage Mr Cameron’s reputation during his second term as Prime Minister.
However perhaps more damaging politically is the suggestion that he knew in 2009 that Lord Ashcroft, a major Conservative party donor, had “non dom” status and therefore did not pay UK tax on overseas earnings.
In March 2010, after it was publicly revealed that Lord Ashcroft was a non dom, there were claims he was attempting to influence a British election while keeping his assets abroad.
When the story broke, Mr Cameron’s spokesman said the Prime Minister had only known for a month, but Lord Ashcroft’s book claims he was made aware the year before.
Mr Cameron has refused to say whether he took drugs at university, only insisting he had not taken cocaine since becoming an MP in 2001. In an interview after being elected leader of the Conservative party in 2005, he said: “What is private in the past should remain private.”
It is not the first time he has faced claims he smoked cannabis at university. Mr Cameron would not comment to claims made in a 2007 biography that he was grounded from Eton as a 15-year-old after being caught smoking weed.
George Osborne defended him at the time, insisting the public did not care what political leaders got up to during their youth.
“It's not been denied by David, but he's also said that we are not in the business of saying that politicians can't have a private life before they come into politics,” Mr Osborne said.
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