Wikipedia
"Piggate" refers to an uncorroborated anecdote that during his university years British Prime Minister David Cameron put a "private part of his anatomy" into a dead pig's mouth as part of an initiation ceremony for the Piers Gaveston Society. The anecdote was reported by Michael Ashcroft and Isabel Oakeshott in their unauthorised biography of Cameron, Call Me Dave, attributing the story to an anonymous Member of Parliament who was a "distinguished Oxford contemporary" of Cameron's. Extracts from the book were published in the Daily Mail on 20 September 2015, prior to its publication.
Downing Street sources responded by saying that Cameron would not dignify the anecdote with a response while friends reported him saying that it was "utter nonsense". Cameron said later that "a very specific denial was made a week ago".
Ashcroft and Oakeshott failed to receive a response from the purported owner of a photograph of the alleged incident, and since the extract's publication no corroborating evidence has as yet been produced to support the anecdote.
In an interview, Valentine Guinness, one of the Piers Gaveston Society founders, said that Cameron "may well have attended one of their parties" but as far as he knew he was never a member.