In 1934 the Daily Mail called Oswald Mosley, founder of the British Union of Fascists, “the paramount political personality in Britain”. The BUF was then enjoying a wave of popular enthusiasm and its membership was up around 34,000. Blackshirts marched through British towns and cities, and new recruits were encouraged simply to fall in behind. There was high unemployment in Britain at the time, particularly in the north, and Mosley’s appeal was in part the promise to restore jobs. A charismatic megalomaniac of immense wealth, convinced he was born to rule, Mosley also attracted support from middle-class Tories. They shared his vaunted pride of race, love of country and his commitment to law, order, free speech and “English methods”.

Jews were not admitted to the BUF, but Mosley was not at this time a rabid antisemite. He said national pride had no need of the “delirium of race”. But he came to realise that a movement requires a scapegoat, and that Jews fitted the bill. He said as much to Lord Sieff of Marks and Spencer, in Sieff’s own home, and to his surprise was at once thrown out. Meanwhile BUF marches, meetings and street violence continued unabated, and it was Mosley’s hope that political disorder would eventually precipitate a crisis that would sweep him into power.

It had happened in Italy, and of course in Germany. Mosley had married into a family, the Mitfords, some of whom were on the warmest terms with senior Nazis in Hitler’s inner circle. The Führer was present at Mosley’s wedding to Diana Mitford in Berlin in 1936, as was the most pro-Nazi of the Mitford sisters, Unity.

Diana Mosley, Hitler's angel, dies unrepentant in Paris Read more

It has been evident for some time that a violent element of the American far right identifies closely with the European fascism of the 1930s. These neo-Nazis repeat the slogans and ape the beliefs. They are extreme nationalists. They are antisemitic, anti-immigrant, Islamophobic and racist. Straight-arm salutes and swastikas are displayed with pride, and there’s a readiness among them to march, chant and fight in the streets, even to drive a vehicle at speed into a crowd of anti-fascist protesters.

The demagogue is indispensable to any fascist movement if its members are to be inspired and held firm to their commitment to take to the streets and spill blood. Fascism does not arise from rational sources. It does not require rational argument to sustain its followers. Fascists are deaf to reason. They sneer at reasonable argument. It is the role of the demagogue to arouse and direct their rage towards the scapegoat, most commonly the racial Other.

This was apparent recently in Charlottesville, in the US, and the demagogue who excited the murderous rage that day, and later excused it, was Donald Trump. Trump is still clinging to public office. Mosley, on the other hand, saw his movement flag and fail. Although he was vastly more intelligent than Trump, and of a far higher level of political sophistication, he was not swept into power on a wave of violent disorder, as he had hoped. Instead he was sent to prison when war with Germany was declared in 1939, along with a number of his lieutenants.

That was not the end of it, of course. Fascism is one of those creatures which, once its head has been cut off, soon enough grows another one. Little remembered today is that at the end of the war, with German cities in ruins, Hitler dead and nazism seemingly destroyed, Mosley and his men were released from prison. Undeterred and unrepentant they went straight back to what they’d been doing before the war.

Facebook Twitter Pinterest An anti-fascist rally in New York, a fortnight after the violence in Charlottesville in August 2017. Photograph: ddp USA/Rex/Shutterstock

They marched through the East End of London, where they had earlier found their chief source of working-class support, and also their chosen enemy, the Jews. They held public meetings, speeches were made, the message loud and clear that Hitler had not only been right, but had not gone far enough, and had left “the job” unfinished. Jewish servicemen, returning from war, were at first astonished and then outraged to discover that what they’d fought against was flourishing in their own neighbourhoods. They heard men shouting anti-Semitic invective on the streets they’d grown up in. They found swastikas crudely smeared on the walls of buildings in Bethnal Green, Stoke Newington, Maida Vale, Kilburn and elsewhere. They hit back.

The 43 Club was founded in early 1946. It was comprised, at first, of tough, well-trained Anglo-Jewish former servicemen. These men set about disrupting the public meetings of the resurgent fascist movement. They also infiltrated it, at great personal risk, to gather intelligence – to learn their enemy’s plans so as to then sabotage them. They fought the fascists on the streets of British cities, and attracted increasing numbers to their cause. They were disciplined, principled and restrained. They were highly effective tactically, and didn’t hesitate to use brute force when it was required. By 1949 the fascist movement in Britain was effectively finished. Mosley had moved to France.

Much of this is told by a founding member of the 43 Group, Morris Beckman, in an extraordinary book called The 43 Group: Battling with Mosley’s Blackshirts, published by the History Press. It’s a story of heroic resistance, also a kind of secret history of that rather murky period. I have borrowed heavily from Beckman’s account of that resistance in my new book, The Wardrobe Mistress. It is a novel of the London theatre in those years, and of the simultaneous revival of fascism in Britain. I end the story in a graveyard, with a kind of echo of the Nazi salute. Fascism may at times seem to fade away but it does not die. Whenever it raises its head, as Beckman and his friends understood and as did those protesters in Charlottesville, it must be resisted. Its head must be cut off, yet again.

• The Wardrobe Mistress is published by Hutchinson.