England in 2019. A wannabe Thatcher dethroned, a wannabe Churchill readying in the wings. Welcome to the age of tribute act politics. The policies that Boris Johnson and his rivals will soon unveil will be just as retro; cover version rip-offs, warmed-up Thatcherism, rightwing comfort food to appeal to the most extreme of their fellow MPs, “the dregs of their dull race”, as Shelley might have called them.

But Johnson’s Churchill-lite shtick and Theresa May’s even less convincing Iron Lady routine are only even vaguely viable because they tap into a fantasy version of British history that has contaminated visions of our conceivable future.

John Lydon got it wrong in 1977, when the Sex Pistols warned: “There is no future in England’s dreaming.” He was out by 40 years. England’s dreamtimes show no sign of coming to an end and Scotland, Wales and Northern Ireland are being dragged under with us.

The Brexiters ask us to “believe in Britain” but not the real Britain, with its flaws and contradictions and a history full of inglorious chapters as well as achievement. The Britain we must believe in is an unreal land of distorted memories and colonial amnesia. The Britain that was simultaneously the biggest empire on Earth and the tiny underdog that “stood alone” in 1940, going on to defeat the Nazis with only bit-part assistance from the US and USSR.

This week’s D-day commemorations will, I fear, help reinforce the idea that it was we “wot won it”, further marginalising the history of the Russians on the Eastern Front, who faced the bulk of Hitler’s forces; that fantasy that Britain built an empire yet showed nothing but paternal care to the people whose lands it invaded and bodies it harvested. And by dint of that history, they suggest, we are a demonstrably exceptional people, not subject to the political and economic realities that limit the options of other, more ordinary, nations.

Winston Churchill, Second Army commandant Sir Miles Dempsey and Field Marshal Bernard Montgomery in the destroyed city of Caen, after Allied forces stormed the Normandy beaches on D-Day. Photograph: -/AFP/Getty Images

What’s particularly unusual about all this is that it appeals to millions who are too young to have witnessed the golden age whose passing they so lament. Most of those fantasising about “empire 2.0” or calling upon us to recover our lost “buccaneering spirit” were children during the Second World War and saw only the tailend of empire. They might talk misty-eyed about Britain’s lost power, and the special relationships we once had with nations that happily kicked us out, but for them the last days of the Raj are not a distant memory but a local curry house.

If you want someone to call you a traitor or accuse you of hating Britain, try suggesting that Britain is a normal nation or that our history is remarkable but not exceptional. If you’re feeling really thick-skinned, you could also mention slavery or the violence of empire. You could point out that other nations, the Dutch for example, have managed to come to terms with the fact that their golden age kind of petered out.

The Netherlands is far from perfect, but its people are not dreaming of recovering the “buccaneering spirit” they too once possessed. This would suggest that it is possible to have a heyday and then move on, grow up and get on with your life.

The period from Trafalgar to 1914, during which the British exerted naval and economic dominance over the world, was a consequence of what Enoch Powell (the spiritual father of Ukip) recognised as a “brief conjunction of cheap and invincible sea power with industrial potential”. Dominance is not our manifest destiny, nor our natural place in the world. Yet to even suggest this in the England of 2019 is to provoke fury.

The fog of historical amnesia also hangs heavily over postwar history. Beyond austerity (version 1.0), the NHS, Suez and “you’ve never had it so good”, not much else seems to come to mind. And over the past three years it has looked, at times, that we’re at risk of flunking maths as well as getting a D for history.

A protest in London on 1 November 1956, after the Suez canal attack. Photograph: Mark Kauffman/Time & Life Pictures/Getty Image

Thus the “people’s vote” is routinely described as a demand for a “second referendum”. This would not wash in a country in touch with its history. The referendum David Cameron dragged us into in 2016 was a second referendum. The first was the referendum of 1975. That, too, was an in/out referendum and not, as is often misremembered, a vote to join the EEC – that had happened in 1973. The question in 1975, as it was in 2016, was to leave or remain.

The politicians who now fume that a second referendum would betray “the will of the people” have spent the past 40 years campaigning for a referendum to ignore the “will” the people expressed in 1975, when Remain got 17.3 million votes. The England of 2019 is a nation trapped in a quantum “Brexit-verse” in which one plus one doesn’t equal two and a third referendum is a “second vote”.

If, on 31 October 2019, the fanatics and the Faragists win and we crash out of the EU, that moment, when the borders close, and the markets open, and the truth sinks in, will not be Britain’s “Independence Day”. A hard Brexit would be so damaging to the true interests of the UK that what might follow – if we are lucky – is a great unmasking, not just of the political fantasists and chancers who peddled the great Brexit swindle, but of the historical delusion that empowered them.

The most extreme among the Brexiters are convinced they can ride the chaos and deploy the “shock doctrine” to remake the nation in their ideological image. But awoken from our dreamtimes by the smelling salts of economic reality, Britain might go the other way and begin the process that would see us start to decolonise our history and our self-image. Through such a process, Britain would, in effect, become the last country to leave the British empire. No matter what happens at Halloween, the dangers of England’s dreaming are surely now clear and manifest.

• David Olusoga is a historian and broadcaster