REX FILE PICTURE The shocking claims were made in a new biography, Call Me Dave

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The Prime Minister carried out the act as a student a Oxford University, according to a claim made in a new biography. The story was recounted to the authors by a contemporary of Mr Cameron who went on to become an MP. He reportedly said the pig's head was resting on the lap of a member of the Piers Gaveston Society – a dining club at Oxford – while Cameron carried out the act.

He even claimed that another member of the notorious group has photographic evidence of the alleged act. But the individual who is said to own the picture did not respond to approaches by the authors. The shocking allegation features in Call Me Dave, a biography of Mr Cameron co-written by Tory peer Lord Ashcroft and the journalist Isabel Oakeshott. Mr Ashcroft said: "Perhaps it is a case of mistaken identity. Yet it is an elaborate story for an otherwise credible figure to invent. "Furthermore, there are a number of accounts of pigs' heads at debauched parties in Cameron's day."

PA FILE PICTURE The alleged act echoes the first episode of the Black Mirror

Lord Ashcroft has revealed his bitter rivalry with Mr Cameron was sparked after he was overlooked by a Cabinet position. He donated more than £8million to the Conservative Party, helping them secure two election victories. But Mr Cameron only offered him a junior whip position in the Foreign Office, which was subsequently turned down. Today the Prime Minister's spokeswoman said: "I'm not going to dignify this book by offering a comment. The author has set out his reasons for writing this book. "The Prime Minister is focused on getting on with the job of running the country." The alleged act echoes the first episode of the drama series Black Mirror, in which the fictional Prime Minister has sex with a pig live on TV.

REX The Prime Minister studied Philosophy, Politics and Economics at Oxford

My drug of choice was weed – and I smoked weed with Dave James Delingpole

The book also claims he was part of a "dope smoking group" called the Flam Club at university, according to the Daily Mail. James Delingpole, a friend of Mr Cameron's at Oxford, said they smoked cannabis together while listening to the rock band Supertramp. He said: "My drug of choice was weed – and I smoked weed with Dave." Mr Cameron studied Philosophy, Politics and Economics at Oxford's Brasenose College between and 1985 and 1988.

British Prime Ministers through the ages Wed, May 27, 2015 With a General Election coming up in May, we look back at some of the famous occupants of Number 10 through the ages Play slideshow Getty Images 1 of 53 Winston Churchill (1874 - 1965) was and is a British icon. After a long career in journalism and politics he became Britain's talismanic war leader in 1940, where his stirring rhetoric and leadership would help the nation to overcome the Nazis. Defeated at the 1945 election, he returned to office in 1951. In 2002 he was named The Greatest Briton of all time by the public in a nation-wide survey