As I write it is 3am over there, and only recently has British Twitter’s bewilderment begun to subside. Bewilderment, specifically, at the jawdropping allegations that David Cameron – you know the guy, the Prime Minister of the United Kingdom – once placed his penis in the mouth of a dead pig.

The claim, based on an anonymous source, appears in a new biography co-authored by Lord Aschroft, the super-rich businessman, pollster and former Cameron ally who most recently appeared in New Zealand news when he interevened to keep dambuster Les Munro’s war medals in the country.

The Daily Mail carries an excerpt from the biography, by Ashcroft and Isabel Oakeshott, including the following explosive passage about the future PM’s Oxford years:

Cameron… got involved in the notorious Oxford dining society, the Piers Gaveston, named after the lover of Edward II, which specialises in bizarre rituals and sexual excess.

A distinguished Oxford contemporary claims Cameron once took part in an outrageous initiation ceremony at a Piers Gaveston event, involving a dead pig. His extraordinary suggestion is that the future PM inserted a private part of his anatomy into the animal’s mouth.

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.

A single, anonymous source is hardly rock solid evidence, especially in an unauthorised biography from a man reported to have fallen out with Cameron before the last election, and the Guardian, for example, has not at the time of writing run anything on the story, but none of that stopped Twitter chasing the comedy.

If you could navigate your way through the gloating and ribaldry, there were some A-grade gags, including “Bae of Pigs” and “the Prosciutto affair”. Inevitably, a spoof Cameron’s Pig account sprung up in no time too. (I suspect you didn’t need telling that it is a spoof account and not in fact an account being run by a dead pig, but there you have it.)

And yet perhaps the whole thing is a twisted tribute to Lyndon Johnson, and a story – itself very possibly apocryphal –  related by Hunter S Thompson, in the course of a discussion about a form of “dirty politics”, no less, that obliges candidates to go constantly on the defensive.

This is one of the oldest and most effective tricks in politics. Every hack in the business has used it in times of trouble, and it has even been elevated to the level of political mythology in a story about one of Lyndon Johnson’s early campaigns in Texas. The race was close and Johnson was getting worried. Finally he told his campaign manager to start a massive rumor campaign about his opponent’s life-long habit of enjoying carnal knowledge of his own barnyard sows.

“Christ, we can’t get away with calling him a pig-fucker,” the campaign manager protested. “Nobody’s going to believe a thing like that.”

“I know,” Johnson replied. “But let’s make the sonofabitch deny it.”

Meanwhile, did Ashcroft have his claims in mind three months ago?

Ashcroft’s view when working on the biography:</p> <blockquote class="twitter-tweet" lang="en"><p> My work station in Auckland New Zealand&#8230;.. <a href="http://t.co/x73s2f0Yfh">pic.twitter.com/x73s2f0Yfh</a> — Lord Ashcroft (@LordAshcroft) <a href="https://twitter.com/LordAshcroft/status/587839612887805952">April 14, 2015</a> </p></blockquote> <p><script src="//platform.twitter.com/widgets.js" async="" charset="utf-8">

As Charlie Brooker and thousands of others noted, gobsmacked, it all had echoes of an episode from his dark comic television series Black Mirror.

For Cameron and his spin doctors this is quite a pickle. There is talk of photographic evidence, and however unlikely that might be, a denial is therefore risky without complete confidence there’s no way any such thing happened. In this sort of scenario, you really don’t want to be caught telling, ahem, porkies.

While we await sunrise in Britain and some sort of statement, or non-statement, from Downing Street, this much can be safely said: the inappropriate contact with a pigtail that landed the New Zealand prime minister in a sticky spot is as of nothing compared to his British counterpart’s problem: an inappropriate-contact-with-a-pig tale.