Taking on your own side is the hardest task in politics. We are a tribal species with inhibitions against giving comfort to supposed opponents. Partisan men and women don’t let the side down, not least because they do not want to find themselves on the receiving end of the special ignominy tribes reserve for traitors and apostates.

So deep does the desire to appear united run, social democrats pretend even now that “Labour is a family”, while all around them far leftists spit abuse. As late as February David Cameron still believed Conservatives could treat each other with “mutual respect” , while all around him an alliance of opportunists and nationalists was preparing to wreck his premiership and what prosperity we have.

If historians want to understand the crisis that has dissolved the Labour party and our links to Europe, they should look first at the dogs that did not bark – the men and women who preferred to put tribal unity before the interests of their country, their party and their own integrity.

I first became aware of the dangers of conformity during the Iraq war. I supported it for what I assumed were leftish reasons. I felt honour-bound to show solidarity with the Kurds, who had been victims of genocidal attacks by Saddam Hussein. And with the Iraqi socialists and trade unionists, who suffered under a regime, which from its gassing of ethnic minorities, via its imposition of a terror state, to its cult of the supreme leader, was authentically fascist.

Everyone I knew disagreed, for the good reasons Sir John Chilcot reminded us of last week. That would have been that were it not for one problem. The great anti-war movement, so venerated by the modern left, was led by George Galloway, a revoltingly sycophantic flatterer of Middle Eastern tyrants, and the Socialist Workers party, which had abandoned what beliefs in secularism and feminism it possessed and allied with the local branch of the Muslim Brotherhood.

So what, many said at the time. The monstrosity of invading a country without having a clue what to do next, the failure to find weapons of mass destruction, the toadying to a braggart of an American president and the willingness to send ill-equipped troops to their deaths, were provocations enough. More than enough.

Who cared about the strange alliances of the far left and far right? What did they matter?

They would not have mattered if the second Iraq war had been the end of it. But as the century progressed, everywhere you looked, you could see what we now call the regressive left growing. Its central tenet was that any religious doctrine, however reactionary, and any dictatorship, however fascistic, could be tolerated as long as it was anti-western.

When I and others argued against the flight from principle to double standards we were denounced, not just by our opponents but by the liberal-left mainstream we were trying to save from its own worst instincts. I am unlikely to forget the moment when, after I published a book on the subject, a BBC producer phoned to say that his idea of a balanced debate was to bring in six people to argue against me.

Nor can I erase from my mind learning at the New Statesman, then a wholly owned subsidiary of the Brownite faction, that its proprietor did not approve in the slightest of criticism of the regressive left. The result of the failure to confront the growing darkness on the left was that, when Jeremy Corbyn came for Labour, not one of his opponents had a coherent argument to oppose him with.

Where are Gordon Brown and all those other BBC-watching and New Statesman-reading grandees of the last decade? Corbyn is destroying their party. It is so unable to oppose the Conservatives it cannot staff its own frontbench. While Labour is led by the most regressive of leftists, a supposedly “decent socialist” who nevertheless took money from, or provided fawning commentary for, the propaganda channels of kleptomaniac, homophobic and imperialist Russia and theocratic, misogynist and homophobic Iran , the Conservative right has taken the opportunity to run riot and run us out of the EU.

David Cameron is the Tory Brown. Like his predecessor as prime minister, he must look on the ruins of everything he once took for granted. He too backed away from a necessary confrontation when fighting might have made a difference – and left the rest of us to pay the price. In 2006, Cameron described Ukip members as “fruitcakes, loonies and closet racists”. In 2013, he retracted, after Boris Johnson, in one of his rare moment of honesty, pointed out that the same words could be used to describe many Conservative voters and MPs. At first, Cameron could not make the argument for the EU because he was pretending that he was still willing to leave if he did not receive concessions from Brussels. Throughout the campaign proper, he bit his tongue for fear of provoking an irreparable split in his party.

Cameron is the Tory Brown. He must look on the ruins of everything he once took for granted

What did for both the European cause and the Labour party was a smug view of British or, more properly, English, history. We are a stable and safe society, it ran. We have not had a truly devastating invasion since 1066 or a civil war since 1660. Unlike virtually every country in Europe, we were not invaded by Hitler or Stalin and never had mass fascist and communist parties. This lucky history has been a curse as much as a blessing. It left us wholly unprepared for the fight against the extremists of the 21st century. We thought that they were just putting on an act. They could not mean what they said and, even if they did, they would never win.

Now they are winning and we can see the ruins of English complacency around us. In the Labour party at least, MPs are preparing to fight back and take the moral as well as the electoral case against the far left to the members. They suspect the Labour cause is doomed, but if they are going to go, they will go fighting.

I speak from experience when I say that they will be met with extraordinary venom. They should not worry about that. At first, you are shocked by the rage of your “comrades”. Then you expect it. And then you come to enjoy it. “On an occasion of this kind,” said Oscar Wilde, “it becomes more than a moral duty to speak one’s mind. It becomes a pleasure.”

Late in the day, perhaps too late, they may yet find the courage to enjoy the pleasure of speaking without inhibition.