Nazis have taken over London – on screens at least. The BBC’s absorbing new series SS-GB, based on Len Deighton’s popular 1978 novel, imagines a world in which the Nazis have invaded and defeated Britain by 1941.

Such an imaginative conceit is by no means unusual. Similar dystopian visions of Nazi victory in the Second World War have long been popular. Take novels such as Robert Harris’s Fatherland (1992), Stephen Fry’s Making History (1996), Philip Roth’s The Plot Against America (2004) and CJ Sansom’s acclaimed Dominion (2012). There was even Iron Sky, the 2012 film which imagined that the defeated Nazis fled to the other side of the moon in 1945 only to plan a space fleet to return to conquer Earth some 60 years later.

As the academic Gavriel Rosenfeld has eloquently argued, persistent rewriting of history is intimately connected to changing perceptions of the Third Reich’s real historical legacy as well as to subversive efforts to “normalise” the Nazi past in the West, and especially in the United States and Britain. Through imagining a life of defeat and occupation, Britons and Americans (who have authored, read or viewed the vast majority of these visions) are able to bathe in the still-lingering glow of victory while at the same time closing the distance between themselves and their wartime enemies.

This nightmare of a Nazi military victory – and of a Nazified world order – was in fact first explored in pre-war fiction, most notably Katharine Burdekin’s Swastika Night (1937). But it was not until the Cold War that the idea took hold, with a flurry of activity in the early Sixties.

The 2012 film ‘Iron Sky’ tells the story of a group of Nazis who fled to the Moon after their defeat in 1945 and plan to return to power in 2018

The year 1964 saw The Other Man air on ITV (with Michael Caine in the lead role) and 1965 the cinematic release of the powerful and provocative It Happened Here. Using deliberately grainy 16mm black and white film, this latter production offered a harrowing portrayal of what a Nazi occupation of Britain might have looked like.

In the United States, meanwhile, the most powerful vision of a Nazi victory was surely Philip K Dick’s 1962 story The Man in the High Castle. Set contemporaneously, Dick describes an America occupied in the West by Imperial Japan and in the East by the Nazis. The two victors of the Second World War are technically at peace, but tensions are mounting, particularly once the Japanese government learns that their Nazi “allies” may be developing new and terrifying weaponry in order to secure overall control of the North American continent.

Tellingly, these Sixties stories are once again very popular. Dick’s frightening vision is the subject of a current Amazon Prime TV series, now in its second season. Similar imaginings have featured in the NBC series Timeless (2016), which features an episode given over to a rewriting of the Second World War, while the 2011 Welsh film Resistance (starring Michael Sheen) begins with the failure of D-Day and the subsequent German invasion and occupation of Britain.

The BBC’s adaptation of SS-GB is just the latest in this line. Clearly, alternative histories of a Nazified world again have commercial and cultural traction.

Rufus Sewell plays a Nazi in ‘The Man in the High Castle’, which imagines North America as if the Nazis had won the war

Perhaps unsurprisingly, the ideas and images offered by such a counterfactual Nazi world seem to have worked their way into contemporary political discourse.

Amid the ongoing cross-Channel rancour connected to Brexit, Boris Johnson, the Foreign Secretary, asked whether the French President François Hollande’s function within the EU was akin to a Nazi prison guard. And during a recent Twitter outburst, Donald Trump responded to his antagonists (in the media and intelligence community) with a pointed question: “Are we living in Nazi Germany?”

Seen in this context, the contemporary fascination with counterfactual history is the popular culture counterpart to Trumpian political “truth”. In Trump’s pronouncements and press conferences, truth is invented and reinvented on a daily basis. Media critics are Nazis; civil rights leaders once battered by the baton are “all talk”; the families of heroic veterans can quickly become villains; and famous abolitionist Frederick Douglass is even resurrected from the dead.

A scene from 1965’s ‘It Happened Here’, which depicts a Nazi occupied Britain

On TV, meanwhile, history is remade and reimagined via the most persistent Anglo-American “what if” nightmare – Nazi victory. The popularity of this kind of television history in the “post-truth” age of fake news surely makes perfect sense: they are two sides of the same coin. While very different in purpose and power, both are suggestive of a world in which the lines between fact and fiction are increasingly blurred. But the apparently symbiotic connection between the two should also give us pause for thought, particularly when the last age of counterfactual fascination – the Sixties – is kept in mind.

Now, beware a spoiler. At the very end of his story, Dick confronts the reader with a revelation. The “reality” of an Axis victory is a myth, and the counterfactual histories of Allied victory authored – to Nazi irritation – by the mysterious “man in the high castle” are instead the “truth”. It is a skillful plot device, arresting and jolting. It also invites a troubling thought: if the “man in the high castle” writes the truth from deep within a myth, what does this mean for Dick’s own relationship with – and to – the 1960s? Does it suggest that Dick was similarly in a high castle and that his counterfactual vision of Nazis in New York contained a “truth” of sorts?

Dick’s contemporaries later endured the age of Nixon, witnessed frequent racialised brutality targeting African-Americans in the south, and encountered – and perpetrated – the massacre of My Lai in the Vietnam War (which one American soldier later admitted was a “Nazi kind of thing”).

As we enter our own counterfactual age, in which truth is twisted and lies disseminated, the renewed obsession with “alternative histories” provides a powerful cautionary reminder of what can happen when nightmares are made real.

Sam Edwards is senior lecturer in history at Manchester Metropolitan University. This article was originally published in The Conversation