On 23 June 2016, the British voter changed. Before that day, they picked a party, usually red or blue. By that morning, only two tribes mattered: remain or leave. And they kept mattering long, long after the result was declared. Rather than bin those short-lived and now stale allegiances, voters made them their personas. No longer a “Labour man” or a “Conservative family”, they became instead “remoaners” or “Brexiters”. Even today, 60% of Britons still identify themselves by where they scrawled a single cross in a one-off poll 10 years ago.

Ask about the difference Brexit has made and the answer normally concerns policy or high politics: how our economic trajectory has become bumpier, or how the Tories keep getting into punch-ups with each other. But it became so much bigger than Boris v Dave. The civil war blazed through the country, and recruited nearly all of us to one side or the other. The effects still ripple through our elections and media today.

Before the murder of George Floyd or the arrival of the Covid vaccine, contemporary Britain’s most powerful form of identity politics was Brexit. Before Gaza, it was the event that radicalised a generation of voters. Without the referendum, you have no GB News and definitely no The Rest Is Politics. There are neither “centrist dads”, nor any “gammon” heckling at the panel on Question Time. Nigel Farage and Zack Polanski aren’t topping the polls or preparing for triumph in next month’s elections. And racism Tommy Robinson-style remains a fringe pursuit. The history of each of these aspects of today’s Britain runs through the summer of 2016.

Our evidence comes from a new book by politics professors Sara Hobolt and James Tilley. In Tribal Politics: How Brexit Divided Britain, they conducted and analysed surveys of large numbers of voters over many years. Put........

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