The BBC likes to say that, when a really big story breaks, the nation turns to the corporation for its take on the news.

Not now it doesn’t. Not when #piggate has dominated social media all day, not to mention the front page of the Daily Mail, which is serialising Lord Ashcroft’s account of David Cameron’s alleged excesses as an Oxford student.

BBC News has just published its version of the story, leading on Lord Ashcroft’s claims that the book is “not about settling scores”, even though it so obviously seems to be. But search the BBC story for “pig” and you’ll find nothing.

The public service broadcaster hates this kind of territory. It’s too squeamish to even mention the anecdote, referred to by Lord Ashcroft and co-author Isabel Oakeshott as “an outrageous initiation ceremony… involving a dead pig” at Oxford’s Piers Gaveston dining society. The two authors report the claim that “the future PM inserted a private part of his anatomy into the animal’s mouth”.

Yes, of course it’s icky and you can understand the BBC’s reluctance to carry anything so revolting on its home page or bulletins. But it is the pig part which is the story here, not the wider and well-known fallout between Cameron and Ashcroft. Piggate is just the kind of disgusting dirt that the right-wing tabloids would love to unearth as they snuffle around in the past of Jeremy Corbyn.

They’ve already run with the Labour leader’s ancient dalliance with Diane Abbott and hazy anecdotes of naked romps in a Cotswold field. The Sun had to apologise after publishing a historic allegation that Corbyn paid £45 to an IRA man, a tale that was revealed to be false nearly three decades ago.

So there’s the BBC’s dilemma. At a moment when it is being lumped together with the newspapers as being part of a broad media conspiracy to wreck Corbyn’s chances before he has even got started, it seems to be turning its nose up at a grubby tale supposedly about the Tory leader.

The decision is further complicated by the hesitance of other news broadcasters, particularly Sky News, which has also avoided the story. But ITV News, which refers to “salacious” allegations that involve “a dead pig” and LBC have been bolder.

Corbyn supporters have already rallied over 80,000 people to sign an online petition calling for the BBC to refer to Mr Cameron as “the right-wing Prime Minister”, in the way that it talks of the “left-wing Labour leader”. These tales of alleged debauchery will only add to that sense of Mr Cameron being a long way further from the middle ground that he often claims to occupy. And the BBC’s failure to specify them will bring further claims of bias.

The BBC’s coverage of the Middle East and the Scottish Independence referendum have also recently drawn accusations of partiality.

Despite a recent softening of tone on the BBC by the Culture Secretary John Whittingdale, the broadcaster’s future remains in the balance and it is extremely conscious of its relationship with Government.

But the most-important part of the BBC’s publicly-funded output is news and it’s unacceptable for it to dodge the big political story of the day. No matter how mucky.