When the anniversary comes, later this month, few will be in the mood to look back. All the political talk will be of the Makerfield byelection, of the future of this government and this prime minister. And yet, it would be wise to reflect on what happened on 23 June 2016 – if only because the choices Keir Starmer and his would-be successors face, indeed the entire political and cultural landscape we now inhabit, are informed or were shaped by that event. We are living in Brexit Britain.

A useful prompt comes from an upcoming two-part BBC series Brexit: A Very British Civil War, made by the master documentarian Norma Percy. Speaking to (nearly) every key player, it brings it all back – the red bus, “take back control”, the pantomime river battle of Nigel Farage v Bob Geldof.

It reminds you of things some may have forgotten, including the extent to which this whole thing came about as a wheeze, a clever tactical ploy, plotted by the careless people who were then running the country. In 2013, David Cameron and George Osborne sought to placate noisy Eurosceptics in their own ranks by promising an in/out referendum after the next election – a pledge they assumed they’d never have to honour because they were sure they’d fail to win an outright majority in parliament, whereupon they would cheerfully trade the promise away as a concession to the Lib Dems.

As if that were not cavalier enough, Britain’s place in Europe became dependent on the soap-opera dynamics of the Notting Hill set: it was all tennis in Regent’s Park and weekends at Chequers, Michael (Gove) letting down Dave and what will Sam (Cameron) think of Boris. Johnson insists he didn’t “give a fuck about being prime minister,” while Osborne begs to differ: “It was nothing to do with the EU, Britain’s place in the world. It was Game of Thrones. That’s what Boris Johnson was playing. And he could see the Iron Throne right there about to be vacated.” This stuff was all-consuming at the time – and yet what was at stake, as these Etonians worked out their schoolboy rivalries, was nothing less than the destiny of the UK. That recklessness with the futures of 70m people remains unforgivable – and the guilt belongs to Cameron and Osborne almost as much as to Gove and Johnson.

More important than the origin story, however, is the legacy. We see that around us every day. Start with the economy. The remain campaign was mocked at the time as “project fear”, spreading gloom by warning that Britain outside the EU would be poorer, to the tune of 6% of GDP. Yet here we are a decade later and, if anything, remain was not pessimistic enough. The drop in GDP is now estimated to be between 6% and 8%, with investment down by as much as 18%. Trade is on course to be 15% less than it would have been had we stayed in the EU, according to the Office for Budget Responsibility, while a staggering 85% of those who import or export goods report problems that they didn’t have before. Remainers said that Brexit would be a slow puncture, as the air was let out of the British economy. So it has proved, except it’s not been that slow.

Brexit’s other legacy, besides upending the old Labour-Tory duopoly, is not measurable in pounds or percentages but is just as real. It is visible in the coarsening and darkening of the national conversation, in the aggression and even hatred that, previously pushed to the margins, now loiter in the centre of the public square. This week the leader of the party that brought us Brexit warned of civil war.

It would be wrong to cast the referendum as the sole cause of this shift – Brexit was, in part, a symptom of the change – and we can all see the role social media and the likes of Elon Musk have played in degrading the discourse. But Brexit both accelerated and intensified that process.

An insouciance towards the facts – recall that “post-truth” was Oxford Dictionaries’ word of the year for 2016 – was an enduring gift of the leave campaign. Percy’s documentary lays bare the knowing dishonesty of the claim that the UK was sending £350m to the EU every week, a gross figure – in every sense – that did not include the more than £80m that came back as a rebate or the money the EU spent in the UK. Johnson’s adviser Dominic Cummings would later brag that “The point of using that really was to try and drive the remain campaign and people running it crazy” – deliberately tangling up his opponents in dry factchecking over stats, while he could press the voters’ hotter buttons. “Love that bus,” an unrepentant Johnson says now, describing it as “the bus of truth”. In 2026, we wade through a swamp of lies and disinformation all the time, especially online – but it was the referendum that drove us into that swamp and at top speed.

The currency of Cummings, Farage and the rest was fear and loathing. We see again Farage’s “breaking point” poster, with its brown-skinned men apparently massing on our borders, and the wholly bogus Vote Leave ad suggesting that 76 million Turks would soon be able to come into Britain via the EU, leaving a trail of dirty footprints behind them. These were racist and xenophobic messages, barely veiled – and they worked.

So it’s hardly a surprise that, a decade later, we have the man who could well be in Downing Street after the next election – and who, tellingly, speaks of Brexit only rarely these days – complaining of “anti-white prejudice” and calling for “pure cold rage” after the murder of a young white man, even as that man’s parents pleaded for his death not to be used to turn Britons against each other. Restore Britain, a party that is endorsed by unabashed white supremacists and neo-Nazis, is on the ballot in Makerfield and might win 10% of the vote. There had always been a far right in Britain, but it used to be confined to the fringes. Brexit invited it in.

By dividing us down the middle, leave or remain, Brexit polarised our politics in a new, starker way. Looking back, it’s clear that remain could never win a contest like that because it was never really about British membership of the EU. In effect, the question became: “Do you want things to remain as they are, or would you like to leave the current reality of your life for something better?” In that contest, there was only ever going to be one winner.

What’s more, the remain cause was doomed by timing. Had the vote come now, in a world menaced by Donald Trump and Vladimir Putin, the folly of standing alone, apart from our nearest neighbours, would be clear. But Trump was a mere candidate in June 2016, and Ukraine was uninvaded. The geopolitical lunacy of Brexit was not as obvious then as it is now.

It’s a tragic tale – a once-confident nation making such a fearful, self-harming decision. Our economy, our politics, our daily lives in 2026 – all of it bears the imprint of that calamitous error. But this story is not over. The BBC documentary confirms the sheer determination that enabled the Brexiters to turn a lost, eccentric cause into a winning movement. All told, it took the leavers 41 years, from 1975 to 2016, to reverse our first vote on EU entry. Rejoin is already the settled preference of a majority of Britons, 56% to 35% at the most recent count – and besides, politics moves twice as fast now. If that calculation is right, and it will take 20 years to overturn the verdict of 2016, we should not lose heart – after all, we’re halfway there.