In what moral universe is the statement “I wouldn’t even rape you” categorised as “satire”? For this is how – in an interview on Sunday with the BBC’s Andrew Marr – Gerard Batten, Ukip’s leader, described a tweet sent to the Labour MP Jess Phillips in 2016 by Carl Benjamin, now one of his party’s principal candidates in the European elections.

According to Batten, Benjamin is a “classical liberal”, “not a bad person”, “a proponent of free speech” and “wasn’t actually making a literal statement”. And there we were, thinking that he was just a vile misogynist, using social media to declare whether, in his opinion, a member of parliament should be raped or not.

That Johnson plays fast and loose with the facts isn't breaking news. More intriguing is the Telegraph's defence of him

Satire and irony are part of what makes life worth living. They are deeply embedded in the British psyche, and the way we describe ourselves and the everyday absurdities we all encounter.

But Batten’s defence of Benjamin was both a monstrous abuse of language – he really should borrow a dictionary – and, even worse, a cowardly attempt to present words of sexual violence as sparkling wit. It reminded me of Ece Temelkuran’s warning, in How to Lose a Country, not to allow politics to be subjugated to comedy, not to push “the idea of the carnival too far”.

The partition between satire and literal speech is certainly growing ever more important, as the right seeks to ensure that it is conveniently blurred. Last week, the press regulator Ipso ruled that Boris Johnson had breached accuracy guidelines in his Telegraph column when he asserted that a no-deal Brexit was the public’s preferred option for leaving the EU “by some margin”.

That the former foreign secretary plays fast and loose with the facts is scarcely breaking news. More intriguing was the Telegraph’s defence of its star writer. Johnson, apparently, was “entitled to make sweeping generalisations based on his opinions … [the column] was clearly comically polemical, and could not be reasonably read as a serious, empirical, in-depth analysis of hard factual matters”.

This preposterous claim would be merely comical were it not so close to the bone. As the Tory party agitates afresh for Theresa May to step down, there is a decent chance that there will be a leadership contest in the not too distant future, and a no less decent chance that Johnson will win it. Which is to say that he will become prime minister, first lord of the Treasury and keeper of the nuclear codes.

If that happens, I would quite like to know which of his statements are (to borrow the Telegraph’s language) “comically polemical”, “sweeping generalisations” or “serious” and “empirical”. These distinctions can mean quite a lot when you are running the country.

Remember when the tech billionaire Peter Thiel said that we should take Donald Trump “seriously but not literally”? In other words: we should acknowledge his political impact but not assume that what he said was a statement of fact or precise intention.

Yet the experience of Trump’s candidacy and presidency has shown that this apparently clever distinction isn’t a distinction at all. When he urges his supporters to “knock the crap” out of hecklers, or praises them for “punching back”, or longs for “the old days” when protesters were “carried out on a stretcher, folks”, it is routinely claimed that he is joking.

But is he? Can anyone claim, with honesty, that Trump’s rhetoric has not contributed to the antagonism, distrust and simmering violence of American political culture today? He may not have personally lit the flames of the Charlottesville riots. But he certainly supplied the oxygen.

Play Video 2:10 'No more Mr Nice Guy': Nigel Farage launches Brexit party - video

Nigel Farage, in March 2017, pledged to “pick up a rifle and head to the front lines” if May did not respect the referendum result. At the launch of his new Brexit party last week, he raged that he would “put the fear of God into our members of parliament in Westminster”.

Predictably, the charge that this language is inflammatory is met with scornful denunciations of liberal snowflakery. But – as in the US – it has been appalling to chart the increase of death threats sent daily to MPs such as Diane Abbott, Anna Soubry, David Lammy, Stella Creasy, Luciana Berger and all too many others. The murder of Jo Cox in June 2016 still looms horribly over Westminster – as well it should. Indeed, the atmosphere around the parliamentary estate, where Britain’s answer to the gilets jaunes (yellow vests) now gathers, is as feverish and intense as I can remember. It is naive to deny that there is poison in the air.

Can one prove, beyond doubt, a causal link between the increasingly aggressive language of the right and this simmering mood of barely suppressed violence? Of course not. But the correlation seems more than coincidental, does it not? In any case: in such febrile times, as the future trajectory of the country hangs in the balance and the political temperature soars, those who would represent or govern us have an accordingly greater responsibility to speak with care.

Beware politicians who confuse free speech (the absence of prior-restraint censorship) with civic recklessness (the casual tossing of matches on to tinder). Beware, too, those who excuse lies, or threats, or hatred as “satire” and posture as the victims of po-faced “political correctness”, even as they stoke up trouble. So much is at stake in the present crisis, so much more than Britain’s relationship with the EU: and high on that list is, or should be, the defence of language itself.

Matthew d’Ancona is a Guardian columnist