The far left cannot face up to rape and its ignorance is killing it. The willingness to excuse the humiliation of women has already destroyed the reputations of Julian Assange and George Galloway. Now it is destroying the Socialist Workers party, which is not only Britain's largest Marxist-Leninist group but the most unscrupulous gang of hypocrites I have ever met.

The SWP's crisis began when a woman member alleged that a senior figure in the party had raped her. The SWP refused to name this hero of the proletarian vanguard; unlike the "bourgeois courts", revolutionary socialists hide the identity of alleged rapists. Nor did it call the police. Instead, it sent the man it called "Comrade Delta" to the SWP's disputes committee. The seven "judges" had no independent evidence – how could they when they were a bunch of Trots rather than a competent court? Nor were they impartial. They knew the "accused". They valued the "leading role" he had played in the party. And they acquitted him.

Friends of the woman say she feels "completely betrayed". Party loyalists have increased her despair by whispering that she was a conniving harlot.

That's the way it is on the far left. The hierarchical party always has the potential to become a rapist's playground. Consider the predator's opportunities. The rank and file has to obey the party line without question. The leaders of political cults, like their religious counterparts, increase their power by fostering paranoia. Members can trust no one outside the party, especially the police and judiciary. The SWP says that Comrade Delta's alleged victim was free to go to the police and chose not to, but party dogma insists that justice is impossible in bourgeois courts. Only when it's too late do women learn that the alternative disciplinary system of Marxist-Leninists exists to control them and let the leaders do as they please. The parallels with the Catholic church are too obvious for me to labour.

Anna Chen saw the misogyny up close. She stopped working as a comic and poet in the early 2000s to devote every waking hour slaving for the Socialist Alliance, Stop the War and other SWP front organisations. "Because the revolution comes first, human beings are just disposable," she told me. "I was struck by how sexless and ugly the leading men in the SWP were. But they always had women. If you slept with one of them, they promoted you. It was as basic as that."

Before the Socialist Workers party, there was the Workers Revolutionary party. Thousands went to its rallies in the 70s, drawn by the presence of Vanessa Redgrave and her late brother, Corin. The party was nothing more than a vehicle that promoted the regimes of Saddam Hussein and Muammar Gaddafi – for money – and supplied a stream of women for its supreme leader, Gerry Healy, to enjoy. It fell apart in 1986 when 26 women came forward to describe the "gross sexual abuse" they had suffered at his hands. In a poignant account that has stayed with me, one exhausted party worker described how she realised that she had wasted her life the moment Healy loomed over her.

"He was not listening to a word I was saying. He wanted only one thing from me, my sexual submission. Something inside of me snapped... It was as if everything I believed in was proved in one, revealing second to be false, lies. I, my husband, my children, my comrades had sacrificed so much, had worked so hard for this... animal."

Whenever arts journalists praise Vanessa and Corin Redgrave's "political commitment", I wait for them to explain precisely what their politics entailed. They never do and the silence of the liberal mainstream about the far left is one reason why abuse has flourished. But it's not flourishing now. After all these years, members of the SWP have discovered they have minds of their own and revolted in defence of the rights of women.

On the face of it, the protesters have no grounds to be angry. What kind of outfit did they think they were joining? The SWP wants to abolish democracy and establish a dictatorship. It made a mockery of its claim to be "socialist" when it joined with the Islamist religious right and persuaded the Stop the War campaign to support the "resistance" in Iraq. Its support did not waver when the "resistance" tortured and murdered Iraqi trade unionists, who had every right to expect the western left's support. How can people be shocked when men and women who condone jihad fail to direct the alleged victims of rape to the police? It would be more shocking if they did.

One can make the same argument about Assange and Galloway. Before he scuttled into the Ecuadorian embassy to avoid facing sexual molestation charges, Assange handed secret police forces from Ethiopia to Belarus the names of dissidents who had spoken to the US State Department. Nothing should surprise you about a man who can sink so low. As for Galloway, he has spent his entire adult life planting wet kisses on the buttocks of tyrants. He can dismiss a dozen victims of abuse before breakfast.

But for all its naivety, the assault on left misogyny remains an optimistic moment and not only because you should always listen to people who stand on principle, however belatedly. The far left isn't a separate entity. It is a fairground mirror that reflects the faults of the liberal mainstream in grotesque forms. If even the brainwashed minions of the SWP can rebel, maybe one day timid liberals will find the courage to condemn a "liberal" legal system that, for reasons of political correctness, has failed to prosecute a single case of female genital mutilation.

Many leftwing commentators disagree with me. They point out that the revolt in the SWP is led by Richard Seymour, a puffed-up political hack, who is just as totalitarian as the apparatchiks he seeks to replace. To their mind, the battle in the party is like a battle in the BNP: no good outcome is possible. But a few Labour historians are more hopeful. They believe the SWP is dying and a foul Leninist tradition is dying with it. If they are right, not only will the air on the left be sweeter to breathe, but British feminism will have won a notable battle without the mainstream media even noticing.