UK Prime Minister David Cameron has remained silent on allegations of obscene conduct during his time at a notorious college club.

A new unauthorised biography on the UK PM, co-authored by supposed adversary Lord Michael Ashcroft, claims Mr Cameron engaged in questionable conduct while part of the exclusive Piers Gaveston Society at the University of Oxford.

According to The Daily Mail, this conduct involved illicit drug use and “an ‘outrageous initiation ceremony’… at which the future prime minister ‘inserted a private part of his anatomy’ into a dead pig’s mouth”.

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The Prime Minister’s office is yet to respond to the claims, which reportedly surfaced at an event in June 2014, but were not publicised until this week.

The source, an unnamed UK MP, also said they had seen photographic evidence of the beastly debauchery, although the photos are yet to be uncovered.

“My co-author Isabel Oakeshott and I initially assumed this was a joke. It was therefore a surprise when, some weeks later, the MP repeated the allegation,” Lord Ashcroft wrote in a piece for The Daily Mail.

“Some months later, he repeated it a third time, providing a little more detail. The pig’s head, he claimed, had been resting on the lap of a Piers Gaveston society member while Cameron performed the act.”

But the photograph’s owner did not respond to enquiries for comment.

“Perhaps it is a case of mistaken identity,” Lord Ashcroft wrote.

“Yet it is an elaborate story for an otherwise credible figure to invent.”

Other claims in the book include allegations of drug taking, made by Oxford University friend James Delingpole.

“My drug of choice was weed – and I smoked weed with Dave…” he said.

True to form, the traditionally sensational UK media did not disappoint, debuting the story under the headline: “REVENGE! Drugs, debauchery and the book that lays Dave bare”.

Others went with more succinct titles, including “PM’s ‘ham dunk'”.

Promoting the book in April, Lord Ashcroft wrote: “Call Me Dave will be entertaining, revelatory and insightful. The Prime Minister may not like some things, but I hope he will acknowledge that it is fair. It is intended to be”.

Lord Ashcroft was once an “integral” figure to Mr Cameron’s Tory party, helping save it from financial ruin.

It has long been rumoured that Mr Ashcroft and Mr Cameron had suffered a falling out.

‘Secret, debauched parties’

The Piers Gaveston Society, named after King Edward II’s supposed lover, has a sordid history.

Although referred to as a dining club, the society glamourises excessive drinking and has been described as notorious for its secret, debauched parties.

“These parties are supposedly held in large country houses and are rumoured to involve the consumption of champagne, caviar and illegal substances such as recreational drugs,” one article for the Cherwell stated.

Membership is limited to 12 undergraduates and former members include Mayor of London Boris Johnson, actor and film producer Hugh Grant and the son of the Duchess of Cornwall Tom Parker Bowles.

Mr Cameron was also a member of the infamous Bullingdon Club, one of Oxford’s oldest ‘dining clubs’, founded in 1780.