Even though Jeremy Corbyn and the men and women who support him are often shabby and occasionally reactionary figures, the rarest criticism you hear of them is criticism from the left. Political commentary in Britain runs like water through pipes. Conventional opinion holds that if you are left wing, you support the Labour leadership, and if you are not, you don’t. Even though there is an essential left case to be made against the degeneration of Labour into conspiracy theory and personality cults, authors who make it are ignored because they do not fit into the familiar pattern. More than any formal censorship, this control of thinking is the most effective way of shutting out new arguments. Matt Bolton and Frederick Harry Pitts’ Corbynism: A critical approach is a rare left-wing critique by authors who are virtual Marxists. Inevitably, it has been all but ignored, which is a fault that needs remedying as this rich and urgent work deserves better than that.

I and many others have argued for years that ‘the left’, or to be fair the voices that dominate the far left in politics and culture, became a regressive force after the Cold War. Its leaders allied with and excused regimes that were the enemies of socialism, feminism and liberalism: Iran, Saddam’s Iraq, Milosevic’s Serbia, Putin’s Russia, and Hamas and other clerical fascist versions of Islam. Why its supporters did not care, or even notice, is a question with many answers. Bolton and Pitts’ are worth reading because theirs is an explanation not just of the Corbyn Labour party but of the post-crash West.

Since 2008, the most strikingly successful political movements have evaded the world as it is by blaming voters’ troubles on a simple enemy. David Cameron, George Osborne and Nick Clegg said that the disaster was the result of overspending rather than the collapse of the financial system. As surely as Viktor Orban or Donald Trump, they told a story about an honest, hardworking people, who had been betrayed by a liberal elite (in our case the Labour government) which had lavished their money on scroungers who lay in bed while the plain folk were shaken awake by the alarm that called them to work.

The left wing variant of the undeserving poor, whose greed threatened the honest and cozened people, was the one per cent – the bankers and speculators – who had so rigged the world that it operated as a conspiracy against everyone else. The Brexiters shifted the pieces around the board. Their evil geniuses were no longer members of the Labour government or the organisers of neo-liberalism but the Eurocrats. The undeserving minority, on whose behalf they were rigging the system, was no longer scroungers or the one per cent but migrants who were undercutting wages and taking money from the NHS.

All these reactions to the crash involve a flight from complexity. Just as supporters of Brexit cannot acknowledge that Britain is a part of an interdependent European economy, and that tearing up the compromises our position in the world entails will create enduring damage, so Corbynism has freed the left from thinking about the compromises living in a part-capitalist economy have always imposed on it. Until now, no centre-left government has been able to escape the constraints, and few have wanted to. They have had to acknowledge that there is no conceivable way to find the taxes to fund a decent society without allowing profit and attending to the needs of the business. The two are dependent on each other and conflict with each other. Neither side can walk away. The right must accept in turn that a productive economy rests on a well-educated and healthy workforce, which the wealthy must help pay for, as well as on trading relationships with neighbours, which limit sovereignty.

To say the far left has never understood interdependence is to understate the case. As surely as the Brexit right, its sole reason for existing is its belief that no compromise is desirable, and its function is to “take back control” from the bankers and the parasites.

As Bolton and Pitts observe, the result is a highly personalised and moralistic politics, a thousand miles away from rigorous economic and class analysis. The hook-nosed “Rothschild” is the left’s version of the Polish plumber or layabout scrounger. The symmetry with the Trump and the Brexit movement is close to perfect. All oppose the EU. All admire Putin, and in the case of Arron Banks and Seumas Milne pay homage to the Russian state. We should not be surprised. If you believe that liberal democracy is a sham – a conspiracy that hides the machinations of the real rulers of the world – any attack on the liberal order is better than none.

In their best passage, the authors describe why a dim, unprepossessing man with no noticeable characteristics beyond obstinacy and self-righteousness can inspire the level of devotion as a Trump or a Putin. The true face of the 21 st Iranian state but was he for its oppression of women, gays and religious and ethnic minorities? Unlike Galloway he is too slippery to say. The trick of his supporters has been to alchemise his slyness into modesty. They have elevated the leader’s personal goodness and placed him 'in a higher realm above the tainted institutions and processes of liberal democracy'. If you support him, you too are good. And if you are good you cannot possibly be an antisemite or misogynist or a supporter of barbaric dictators – even though to outsiders you give every appearance of being all of these things.

I’ll give you just one example to make the point. The far left’s anti-Europeanism has convinced it to support the May government’s determination to end freedom of movement. This will be the greatest restriction on the freedom of British citizens to travel, live and work where they choose, and love and marry who they choose, in living memory. It is also a restriction on immigration beside which the efforts of Ed Miliband appear paltry.

And yet while Corbyn’s closest supporters denounced Miliband, words fail them when their master proposes a far harsher regime. The far left justifies itself by dehumanising migrants. They are no longer people but vectors in a system of production that wants to move resources and people around the world, and pawns in a neo-liberal conspiracy that will frustrate the utopia of socialism in one country.

The illiberalism of Labour is ignored, however, by Labour members because the myth of the leader’s unimpeachable integrity means that as ‘a lifelong anti-racist’ he cannot be judged by the same standards as the Labour politicians who preceded him. Indeed, his transparent goodness means that anyone who says otherwise must be prompted by a malign desire to promote greed and oppression. The personality cult thus creates the conspiracy theory: for who except the wicked would attack a saint? For a left that once prided itself on its scepticism and intelligence, the disgrace of this combination of credulity and viciousness will take a generation to live down.

Worse may come. I wouldn’t bet much on the future of the Human Rights Act under a Labour government or the independence of the civil service, judiciary and the BBC. The conclusion of populism is authoritarianism as its simple slogans can never survive contact with reality. As frustration grows, Labour in power will lash out at anyone who might check it.