There’s a very funny moment in Jon Ronson’s book Them: Adventures with Extremists, part of which follows the New Age mental case David Icke on a tour of Canada. All the way across the great plains, Icke has been promulgating his thesis that we are the unwitting subjects of shape-shifting reptilian alien overlords. Aside from Ronson, a protestor has been following Icke, too — demonstrating outside each venue —convinced that when Icke says ‘shape-shifting reptilian overlords’ he really means ‘Jews’. Eventually, having heard Icke speak on perhaps a dozen occasions, Ronson asks the protestor, ‘Do you still think that when Icke says lizards, he means Jews?’ And the protester replies, a little crestfallen: ‘No. He really does mean lizards, doesn’t he?’

People get deranged by stuff and end up thinking we’re controlled by mysterious creatures which are sometimes a euphemism for ‘Jews’ and sometimes perhaps not. I don’t know what exactly deranged Mr Icke. With my colleague Matthew Parris — who seems to be headed on an express train to the booby hatch, with my old friend Nick Cohen checking his ticket and offering light refreshments — it was Brexit and the rise of populism.

In an article for the Times last week Parris gave a rather startling debut to the mysterious creatures jabbering away inside his head: ‘the shadow.’ It was the shadow, a convocation of philistine, pig-ignorant, ill-bred, jingoistic scum which delivered us Brexit and is now busy ushering us into an age of authoritarianism and intolerance.

By which I think he means ‘people who, inexplicably, have a different political opinion to myself’. But the result is the same, a dehumanising of more than half of the country. Not really people at all, just a kind of semi-sentient vast and toxic soup, like something out of The Quatermass Experiment. And having so consigned them, these awful people, their opinions and aspirations can be easily written off.

There are mysterious creatures jabbering away inside the heads of the left wing of the Labour party, too, and most vociferously among its leadership. No euphemism required: these are not lizards or shadows, just Jews, plain and simple. For the Hamas and Hezbollah fellow-travellers among them, it’s because the Jews are a vile and cursed race. ‘Why do you think everyone hates them?’ a half-witted thug from Hamas asked me, rhetorically, in Hebron a few years ago.

For this lot, the total destruction of the Jews cannot come quickly enough. So, for Labour councillor Aysegul Gurbuz, Hitler was ‘the greatest man in history’ and she longed for the day when Iran would wipe Israel ‘off the map’. The party suspended her. Didn’t kick her out, just a slap on the wrist. That in itself should tell you enough about the state of the party.

For the rest, the anti-Semitism is a derangement occasion-ed by the failure of socialism, for which they blame the alleged architects of capitalism, the Jews; by the reassertion of old Cold War allegiances; and by the kind of fashionable attitudinising which insists that Israel is the only state in the world responsible for all the bad things that happen there (in every other state where bad things happen, it’s our fault). This attitudinising is accompanied by a liking for Venezuela, Cuba and, yes, North Korea.

This is a slightly more refined anti–Semitism than that evident in the cheerful Gurbuz tweets quoted above. But it is no less pernicious and hateful. Have you wondered why Corbyn and the Labour party have not fully apologised for having defended a grotesquely anti-Semitic mural which was painted on a wall in the Islamic hell of Tower Hamlets? For the past week or so Corbyn has been hunkered down with his advisers, anxious to stamp out this fire and yet also kind of reluctant to do so.

The reason for this is that they think, actually, they are dead right. They believe Jews are weirdly powerful and control the world’s economy (which of course they do not) and the British media (which of course they do not). They think that dark forces are at work. The anti-Semitism issue has been ‘weaponised’, according to one thick- as-mince Corbynista MP. And who, then, is doing the weaponising?

Well, we know who it is. But best not to say out loud. They are very powerful, these mysterious forces. This is why Lib Dem and SNP politicians can hold a ‘UN Day of Solidarity with the Palestinian People’ and ban a group of Jews from attending. It is why, when anti-Semitic attacks in the UK are reported as reaching an all-time high, the anti-racist organisations can claim the figures are somehow being exaggerated.

These people — Corbyn included — may not sign up to the more fabulously berserk anti-Semitic tropes, such as the blood libel and the fraudulent Protocols of the Elders of Zion (although that being said, Corbyn was indeed a member of a Facebook group which accused Jews of organ trafficking in Syria). But they believe the rest of the rubbish. Jews all-powerful. Jews running everything. Jews with money. Jews up to no good. There were even suggestions on Labour websites that the Jews, in the form of Mossad, were behind the attempted murders of Sergei Skripal and his daughter Yulia. Yeah, of course they were. How could we have been so blind?

Anti-Semitism is no less repulsive or harmful because it has not been occasioned by a religiously indoctrinated hatred and a convenient sense of acquired victimhood. It is anti-Semitism just the same. Incidentally, David Icke thought that in the Protocols of the Elders of Zion, the authors had used the word ‘Jews’ as a euphemism for ‘lizards’. Well, in the secure wards of our mental hospitals, those terms are pretty much interchangeable. Aren’t they, Jeremy?