Citing an unnamed member of parliament, a forthcoming biography of David Cameron claims Britain’s Conservative Prime Minister “put a private part of his anatomy” in a dead pig’s mouth during an initiation ritual as a student at Oxford, the Daily Mail reports.

The Mail began to serialize the book—titled Call Me Dave and penned by former political ally Lord Ashcroft with journalist Isabel Oakeshott—Sunday night, attributing the allegation to a “distinguished Oxford contemporary” who said Cameron performed the act as an inductee into the school’s notorious Piers Gaveston Society:

The source — himself an MP — first made the allegation out of the blue at a business dinner in June 2014. Lowering his voice, he claimed to have seen photographic evidence of this disgusting ritual.

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.

The MP also gave us the dimensions of the alleged photograph, and provided the name of the individual who he claims has it in his keeping.

According to the book, attempts to reach out to the photograph’s owner failed.

“Perhaps it is a case of mistaken identity,” writes Ashcroft. “Yet it is an elaborate story for an otherwise credible figure to invent.”

[Image via Getty Images]