LONDON — “I did not have sexual relations with that pig.”

It’s not the sort of denial any world leader wants to make, and Prime Minister David Cameron has yet to respond to allegations that he once inserted his penis into the mouth of a dead pig.

The bizarre, and possibly illegal act, allegedly took place during the initiation for a debauched and secretive society at the University of Oxford. The lurid details are described in an extraordinary, unauthorized biography of the British prime minister written by the former deputy chairman of the Conservative Party.

Downing Street has refused to comment on the alleged indiscretion, which is being described as his “Bae of Pigs” crisis on Twitter.

Lord Ashcroft’s book also alleges that Cameron was a member of a “dope smoking group” called the Flam Club and repeats rumors that cocaine was allowed to circulate openly at the future prime minister’s home in London. Ashcroft, who gave more than $12 million to the party, accuses Cameron of appearing lazy and unreliable and says his own campaign chief described him as a “posh c***.”

Lord Ashcroft and co-author Isabel Oakeshott—former political editor of The Sunday Times—claim they were told about the pig’s head by “a distinguished Oxford contemporary” who also went on to become a Member of Parliament.

It was claimed that Cameron took part in an initiation ceremony to join the Piers Gaveston society, a notorious Oxford club that takes its name from the reputed gay lover of King Edward II. The magazine Tatler, Britain’s leading arbiter of the aristocracy, describes the group as Oxford’s “coolest” drinking society, with an annual summer party that is “basically a very well-organized orgy.” Hugh Grant was once a member.

The unnamed politician told the authors of Call Me Dave that he saw photographic evidence of Cameron placing “a private part of his anatomy” into the mouth of a pig’s head as it rested in the lap of a Piers Gav member.

Ashcroft and Oakeshott conclude that it would be “an elaborate story for an otherwise credible figure to invent.”

The story is, however, similar to a classic dirty tricks campaign legend described by Hunter S. Thompson in Fear and Loathing on the Campaign Trail ’72.

This is one of the oldest and most effective tricks in politics. Every hack in the business has used it in times of trouble, and it has even been elevated to the level of political mythology in a story about one of Lyndon Johnson ’s early campaigns in Texas. The race was close and Johnson was getting worried. Finally he told his campaign manager to start a massive rumor campaign about his opponent ’s life-long habit of enjoying carnal knowledge of his own barnyard sows.“Christ, we can ’t get a way calling him a pig-fucker, ” the campaign manager protested. “Nobody ’s going to believe a thing like that. ”“I know, ” Johnson replied. “ But let ’s make the sonofabitch deny it. ”

The prime minister’s spokeswoman seemed keen to avoid exactly that Monday, claiming that she “won't dignify with a response” any of the allegations contained within the book. The serialization of Call Me Dave is due to continue in the Daily Mail for the rest of the week, so it remains to be seen how long that line can hold.

Cameron has never denied recreational drug use. The book quotes a friend, James Delingpole, recalling hazy days in his university rooms listening to Supertramp albums under the influence of marijuana.

“I had a room on the top floor, and we’d all sit on the floor and smoke dope,” he claimed.

Delingpole, now a journalist, also described the antics of the university drinking clubs. As well as the alleged association with the Piers Gaveston society, Cameron was a confirmed member of the Bullingdon Club, along with two of the favorites to succeed him as prime minister, George Osborne, the current Chancellor of the Exchequer, and Boris Johnson, the mayor of London.

“What it basically involved was getting drunk and standing on restaurant tables, shouting about ‘f***ing plebs’,” said Delingpole. “It was all about despising poor people… It’s about mindless destruction, and conspicuous excess and the rather ugly side of upper-class life. It’s loathsome.”

Lord Ashcroft, who was once the party’s biggest donor, admits in the book that he has personal “beef” with the prime minister. The two men were once close but fell out when Cameron was elected prime minister and refused to give Ashcroft the job he claims he was promised.

“Long after he became prime minister, the impression persisted that he was more interested in holding the office than in using its power to achieve anything in particular. His laissez-faire approach can create the impression that he is insufficiently concerned by results, and more than once he has appeared so relaxed that he has only stirred to avert disaster at the last minute. But my own particular beef with him is more personal,” Ashcroft wrote.

He said one of the prime minister’s colleagues confided in him that: “Cameron’s word is as good as the paper it’s written on.”