For readers bewildered by the indifference of Labour’s leaders to Brexit, let me offer a suggestion: you cannot understand British politics until you grasp that the party has been taken over by men (and the occasional woman) who spent their lives around the fag ends of the 20th-century Marxist-Leninist movement.

It’s not that Labour now has a communist programme. Revolutionary socialism is as dead as any idea can be. Rather, Labour has inherited the mental deformations of the Leninist style of doing business: the leadership personality cult, the love of conspiracy theory, the robotic denunciations of opponents, and most critically for our current crisis, the ineradicable fantasy that the worse conditions for the masses become, the brighter the prospects of the far left are. Disaster socialism is its alternative to disaster capitalism.

The hardest thing to see is what is staring you in the face. Even now Labour supporters do not recognise that their party had inherited the worst traditions of the far left. Yet how else to explain why Labour wants to end the freedom of movement its young members celebrate and leave the single market on which the manufacturing working class depends? An authentic leftwing party would worry about how a “compromise” Brexit – let alone the threat of leaving without a deal – will hit the poor and traditionally Labour-voting regions of Wales, the Midlands and northern England and extend austerity by cutting the tax base.

It is the embrace of what Leninists once called 'revolutionary defeatism' that is Labour’s most striking characteristic

Labour’s leaders don’t sound remotely fearful, however. When asked about Brexit they deliver bland, mendacious slogans and make it as clear as a waiter trying to avoid eye contact that they would much prefer to talk to someone else. The easy point to make against them is that ending freedoms is what the far left has always done: there was precious little freedom of movement across the Iron Curtain. But, for anyone familiar with socialist history, it is the embrace of what Leninists called “revolutionary defeatism” that is Labour’s most striking characteristic.

Corbyn wrote for the Morning Star, the newspaper of the old Communist party, which managed to carry on being pro-Soviet even after the Soviet Union collapsed. His Stop the War coalition was founded by Trotskyists from the Socialist Workers party and Islamists, an alliance of believers in the one-faith state and one-party state, as some of us noted at the time. Seumas Milne, his director of strategy, was a member of Straight Left, a tiny faction that allied with the hardline communists. Corbyn’s senior political adviser, the Scottish aristocrat Andrew Drummond Murray, was on the executive committee of the Communist party of Britain. Meanwhile, because so few vote in their elections, far-leftists have found it easy to win power in trade unions, Len McCluskey’s dominance of Unite being a case in point.

The few decent people left at the top of Labour understand the consequences. One explained that, whatever other qualities Corbyn possesses, he is not overburdened by the weight of his intellect. The brains behind the operation are John McDonnell, Milne and Murray. And “they absolutely believe that if Brexit brings chaos the voters will turn to the radical left”. To put it in Marxist language, a crisis in capitalism will allow the left intelligentsia to lead the proletariat to victory. Corbyn and McDonnell hardly dare talk about their hopes for fear of alienating pro-European supporters. But it’s clear that they want a Brexit that allows them to deliver socialism in one country, free from EU rules: a utopia they cling to even after leftwing economists have exposed it as an empty fantasy.

The naivety of supporters who refuse to see the influence of far-left ideology on Labour politics remains breathtaking

Lenin established the doctrine of revolutionary defeatism during the First World War. He had no time for “banal” socialists who were campaigning for peace. The true communist welcomed war and yearned for the defeat of his country. For a defeat, in Lenin’s case of Russia by Germany, would incite “hatred of one’s own government and one’s own bourgeoisie” and bring the revolution closer.

The idea has had such a hold on the far left because it allowed the Bolsheviks to create the world’s first communist tyranny. But however dearly the myth of catastrophe leading to socialism is held, there is little evidence since 1917 that economic disaster advances the interests of the European far- or centre-left. The great depression of the 1930s brought the rise of fascism in Germany. The hyper-inflation and trade union militancy of the 1970s did not bring the Bennite socialism the young Corbyn dreamed of, but the long, hard rule of Margaret Thatcher. I accept that the crash of 2008 helped Barack Obama take the White House, but it brought the Conservatives to power in Britain, allowed the triumph of German economic orthodoxy in the eurozone, and helped create the reactionary climate for Brexit itself.

Beyond the practicalities lies the morality. To wish suffering on people who are weaker and poorer than you is disgusting and it is no less disgusting when Jeremy Corbyn rather than Jacob Rees-Mogg is hoping that the misery of others will advance his political programme.

There are many reasons why Labour has no coherent Brexit policy to offer parliament and continues to pretend that Britain can somehow retain the benefits of EU membership while leaving the EU. It is as worried as the Tories are about alienating voters and seeing its party fall apart. Yet the naivety of Labour supporters who refuse to see the critical influence of far-left ideology on Labour politics remains breathtaking.

“When someone shows you who they are, believe them,” said Maya Angelou. The dominant factions of the British far left have shown you since the 1970s that they are anti-European. All far-leftists have shown you since 1917 they believe, despite all evidence to the contrary, that catastrophe should be welcomed as the midwife of socialist revolution. Why not believe them?

• Nick Cohen is an Observer columnist