You could call it Ireland’s sweet revenge, and both the timing and the irony would be historically exquisite. It would come just as Boris Johnson’s reckless government tries to bully Dublin on future Irish customs arrangements and as large parts of the Tory party salivate for a no-deal Brexit that will cast the Irish peace process casually aside. But if the 2019 general election that Johnson craves takes place, it may not be long before, politically speaking, Brexit Britain comes to resemble Northern Ireland.

To understand that this possible Ulsterisation of British politics is a genuinely serious prospect, step back a bit and consider the way that electoral behaviour has been evolving in Britain. Ever since 1964, political scientists, mainly based at Nuffield College, Oxford, have worked on the British Election Study (BES). For more than half a century they have tracked the decline of the old industrial-based two-party system in which general elections were fought between the Conservatives and Labour, who battled for the floating voters in the middle ground across the land.

Today’s electoral politics are fundamentally different. A long-term trend of dealignment from the two big parties means that voters are no longer loyal battalions of partisans. Millions of individual voters are now happy to switch between an increasing array of parties. In 2015, 43% of them voted for a different party from the one they had supported in 2010. In 2017, 33% switched from their 2015 vote. In 2019, a similar kaleidoscopic change seems certain. Tellingly, a BES study of these two recent elections, due for publication in December, will be titled Electoral Shocks: the Volatile Voter in a Turbulent World.

Electoral volatility was already a growing trend in the late 20th century. But Jane Green, one of the study’s authors, says electoral shocks, which have come thick and fast in the 21st century, have accelerated the process. She cites five big ones: immigration and the rise of Ukip after 2004; the 2008 financial crisis and the subsequent recession; the Liberal Democrats’ decision to go into coalition in 2010; Scotland’s independence referendum in 2014; and, finally, the Brexit vote in 2016. Each has reshaped politics and added to the impact of volatility.

The Brexit vote is the mother and father of these shocks, not only in itself but in its prolonged duration. Even today, more than three years on, it is still creating big aftershocks. Failure to leave the EU by the original 29 March deadline helped trigger the Brexit party’s success in the EU elections, and in turn brought down Theresa May. Another such shock is likely when parliament reconvenes on 19 October after next week’s EU summit, and on 31 October, when Britain will again either leave or stay longer in the EU. What happens on the end of the month deadline will rearrange the board.

Few are foolish enough to predict with certainty how a 2019 election will play out. The 2017 election saw a swing back to two-party politics but a significant reshuffling of the two parties’ electoral bases. Two years on that picture has fractured afresh, with the rise of the Brexit party and the revival of the Lib Dems. Today’s unknowns, as Donald Rumsfeld might have said, are still unknown. Tellingly, the most authoritative voice of caution comes from the dean and doyen of British political scientists, David Butler, 95 next week, who told a BES event on Tuesday that in 70 years of studying elections, “I have never felt more totally confused and uncertain” about the outcome. When Butler says that, it is like David Attenborough telling you there is a climate crisis.

Nevertheless, there is now a real possibility that in the next election Brexit will become in England and Wales what the union has become in Scotland: the decisive divide in electoral behaviour. Brexit is important, salient and highly divisive. Overwhelmingly, people are in one camp or the other. This would not mean that other issues, including economic divides, no longer apply at all. But these other issues would tend to be refracted through the prism of Brexit.

That is certainly the view of Johnson and his strategists. They want a Brexit election. So do the Brexit party, the Lib Dems, the Greens and the SNP. Only the Labour party acts as if the election will be about more traditional issues. For some voters, that will be true. But Labour could find its votes shaped by Brexit in spite of its own best efforts because 68% of its 2017 voters are remainers.

But if Brexit is reshaping the electoral battle, it is in reality two separate battles. The Tories and the Brexit party are battling for leave voters, while Labour, the Lib Dems, Greens and nationalists battle for remainers. Very few voters sit in the middle of the road on Brexit or the cultural issues that are so closely associated with it.

Remind you of anything? It should. Northern Ireland has had two electorates for decades. Parties battle in one or the other, leaving slim pickings for those who try to reach across the divide. As Geoffrey Evans, another BES author, put it this week: “British politics is no longer about the battle for the middle ground. It’s become like the Northern Ireland system.” And Evans adds a sobering further thought, that in Northern Ireland the winners are the parties that voters trust not to give in to the other side. “Could the Liberal Democrats be the Sinn Féin of all this,” he wonders.

Northern Ireland’s divides are rooted in centuries of religious divide. The Brexit divide in Britain is far more recent. But it is rooted in identities and anger, too. If Brexit does become the defining issue in mid-21st-century British politics, the hope of a country coming back together could be as fragile as the dream of Irish peace now is, and just as fraught.

• Martin Kettle is a Guardian columnist