LONDON -- A controversial new biography of British Prime Minister David Cameron claims that he took part in an initiation ceremony which saw him place a “private part of his anatomy” into the mouth of  a dead pig.

The unverified claim comes in "Call Me Dave," a new biography of Cameron co-authored by Conservative peer Lord Ashcroft and journalist Isabel Oakeshott, which also suggests there is photographic evidence of the incident -- though the person, who is said to own the image, did not respond to approaches from the authors.

“Perhaps it is a case of mistaken identity,” Ashcroft said in a report by the Daily Mail. “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.”

The incident is said to have happened during a party at the notorious Oxford dining society, the Piers Gaveston, which specializes in bizarre rituals and sexual excess according to the Daily Mail. The book says the incident took place during Cameron's time at Oxford University where he studied Philosophy, Politics and Economics from 1985 to 1988. 

Ashcroft claims the incident was first revealed to him by another Member of Parliament (MP) at a dinner in 2014, though the author at the time thought it was a joke. The same MP repeated the story two more times in the following weeks, revealing more detail to the author. The person, who claims to have witnessed the event, says the pig’s head was resting on the lap of a Piers Galveston society member while Cameron performed the act.

Cameron has not yet responded personally to the claims while Downing Street says it does not recognise the allegations.

Many have drawn comparisons between the claims made in the book and an episode of satirical television show Black Mirror, which first aired in 2011 and shows a fictional British prime minister performing a sex act on a pig in order to save a young girl’s life.

The creator of Black Mirror, Charlie Brooker, has already sought to distance himself from the claims in the book, saying that it was a coincidence.