10 Downing Street is refusing to comment on the allegations about David Cameron and a dead pig

The UK woke up on Monday to allegations that David Cameron, the prime minister, put "a private part of his anatomy" into a dead pig's mouth as part of a university initiation ceremony.

It was an anecdote from a new book about his life obtained by the Daily Mail.

Cameron carried out the act when he was a student at Oxford University, according to the book co-written by Lord Ashcroft and journalist Isabel Oakshott.

The prime minister's office at Number 10 Downing Street was not in the mood to comment on the bizarre story.

Journalists fresh from a briefing tweeted about it. Here's Christopher Hope, chief political correspondent at the Daily Telegraph:

It didn't even get featured in the summary of the briefing, which said: "The Prime Minister's Official Spokesperson answered questions about the Trade Union Bill, EU reform, the independence referendum and Syria."

Meanwhile, George Osborne, the Chancellor of the Exchequer, was asked about it while on a trade mission to China. He tried not to laugh and said "I haven't seen that book."

Ashcroft, a former ally, fell out with Cameron after the prime minister failed to follow through on a promise to give him a top ranking job after winning the 2010 election. The pair now infamously dislike each other.

The book, called Call Me Dave, features a source who claimed to be present during the pig incident and has photographic evidence. However, the book also makes it clear that Ashcroft and Oakshott failed to actually obtain the photo in question. That creates an obvious question of why they published this piece of gossip when they were unable to prove it, and why the Mail chose to repeat it. The Mail is usually (broadly) supportive of the Conservative Party.

The book is out next month and is being serialised in the Daily Mail. The Mail says:

For the first time, the book tells of Mr Cameron's membership of a decadent Oxford dining society, known as the Piers Gaveston.

This was in addition to his time spent with the Bullingdon Club, a drinking society for the super-rich notorious for bad behaviour and trashing restaurants.

The authors report an account of an 'outrageous initiation ceremony' at a Piers Gaveston event at which the future prime minister 'inserted a private part of his anatomy' into a dead pig's mouth.

The story was recounted to them by a contemporary of Mr Cameron who went on to become an MP - and who claims that another member of the group has photographic evidence to prove it.

The unnamed individual said to possess the picture failed to respond to the authors' approaches.

As you might expect, the story is doing the rounds on Twitter. It's more popular even than the Emmy awards.

A parody account called David Cameron's Pig already has 2,400 followers: