The supporters of Jeremy Corbyn are meant to comprise the most cultish movement British politics has seen. Yet on the issue of left anti-Semitism they do not blindly follow their leader. For once in their lives, they give every impression of thinking for themselves.

Corbyn has come as close as he can to admitting a mistake – which by most people’s standards is not close at all. Like Stalin airbrushing his own history, he has deleted his Facebook account. He did not explain how he found himself a member of Facebook groups that featured Holocaust denial, or defending medieval fanatics who believe Jews drink the blood of Christian children, or endorsing Nazi-style propaganda. But he was prepared to say the abuse of Jews and non-Jews (for all you have to do on the far left to become a ‘Zionist’ today is criticise Corbyn) was ‘certainly not in my name’.

His supporters in Momentum spoke with greater moral seriousness. The said anti-Semitism was ‘more widespread in the Labour party than many of us had understood’. (The ‘us’ in that sentence refers to Momentum’s leaders, incidentally, not to ‘anyone with eyes to see’.) Maybe the spectacle of Momentum’s Christine Shawcroft defending a Labour candidate who publicised Holocaust denial changed minds. Or perhaps Momentum’s founder Jon Lansman learned a lesson about modern racism I learned myself years ago. Like black supporters of Donald Trump, Jews on the far left are tolerated as long as they follow orthodoxy. When Lansman stepped away from it by challenging Corbyn’s candidate for the Labour general secretary, his Jewishness had turned from an irrelevance into a total explanation for his character and behaviour. Lansman and his ‘Zionist friends no doubt want a Zionist in charge because they put Israel above the Left or even Britain,’ Corbyn supporters told him on Twitter. Momentum was ‘a vehicle to further his own Zionist takeover of the Labour party’.

For whatever reason, both Corbyn and Momentum have said prejudice must be recognised and fought.

Go to the Labour party forums on Facebook, however, or monitor Twitter and you find dark mutterings about plots by Jews to ‘smear’ Jeremy and help the Tories grind the faces of the poor into the dirt. Instead of being contrite about the fact that Jews and their allies held an anti-racist demonstration against the Labour party last week, Corbyn supporters seized on the presence of Tory MPs as evidence that that Labour MPs at the rally were ‘traitors’.

Quoting tweets leaves you open to the charge of exaggerating the importance of a few cranks and creeps. Look then at the main journals of the far left, which cannot be so easily dismissed.

Corbyn’s old newspaper the communist Morning Star said the ‘self-proclaimed 'leaders of British Jewry'’ were making ‘bogus accusations that Labour leader Jeremy Corbyn is somehow soft on anti-Semitism’. In language horribly familiar to anyone old enough to remember the robotic curses of communism, the paper denounced Corbyn’s critics’ ‘preposterous posturing’. They were engaged in ‘a cynical ploy’ to undermine ‘Labour’s performance at forthcoming local elections’. So there you have it, if Labour loses seats, a Jewish conspiracy will be to blame.

Like the Morning Star, the Canary and SKWAWKBOX never once criticised the adoption of medieval and fascist ideas and images. Even though their leader, in however mealy-mouthed a fashion, has accepted he may have been at fault, they do not admit their mistake. Instead, they cast far leftists as victims rather than victimisers. Or as SKWAWKBOX explained as it shed the tears of the cry-bully.

“ Many people have reported depression, severe mental distress and even suicidal feelings as a result of the unprecedented and undeserved assault aimed at a leader who has given them hope of a change from the predations of the Tory government.

There you have it again. Criticism of Corbyn is a threat to public health. He is the way and the truth and the light, and anyone who is against him is against all hope and goodness.

Finally, a nest of academics sent the obligatory round robin to the Guardian arguing that black was white, two plus two equals five and charges of anti-Jewish bigotry were not based on the hard facts of Jewish experience of life on the left. They were, of course, a plot ‘framed in such a way as to mystify the real sources of anti-Jewish bigotry and instead to weaponise it against a single political figure just ahead of important elections’.

The use of ‘weaponise’ is everywhere on the left and it is a tellingly insidious charge. The militaristic imagery is meant to imply to the faithful that uncomfortable arguments are not the normal business of free societies but acts of war.

There are two possible explanations. The first is Corbyn’s followers are finally breaking with him. Corbyn may have more power over the Labour party than any previous leader, but on anti-Semitism, his supporters will find the courage to defy him.

The alternative is more convincing. His followers do not believe Corbyn is sincere. He only speaks of his concern about anti-Semitism and his determination to do better because it is politically expedient, the smart PR move. In his doublespeak there is one message for worried Labour supporters, and another for his base. Don't worry, he implies. Nothing will change. I am just going through the motions. The desire to send a Trumpian nudge and a wink was the real meaning of his decision to spend Passover with a tiny Jewish group that thinks there is no problem with anti-Semitism.

For a serious effort to combat anti-Semitism would require the far left to purge itself. It would require Corbyn to tell his supporters to stop threatening David Lammy, Thangam Debbonaire and the other Labour MPs who attended the demonstration against anti-Semitism outside Parliament last week. He now admits the demonstrators were right. Doesn’t he? So left wingers cannot censure Labour MPs for standing up for a cause their leader now believes in.

They can because when Corbyn was asked to say Lammy should not be deselected he retreated into doublespeak. At one point he seemed to be telling his followers to back off. At another he said it was ‘it was up to the local party’ and it was no business of his if it ended Lammy’s career.

We will see which side he comes down on when the far left comes for ‘Zionist’ MPs who have ‘weaponised’ anti-Semitism as part of an anti-Labour conspiracy. His supporters think they already know. They are not rebelling but following. They appear to defy the cult leader, while all the time honouring his wishes.