Laura Kuenssberg, the BBC’s political editor, will spill the inside beans of Brexit on Monday: how was it possible for David Cameron to have entered this referendum so unprepared, so lukewarm, when it was his idea in the first place? Was Jeremy Corbyn ineffective because he was indifferent, or was he a perfectly effective campaigner, scuppered by a hostile media? How did Michael Gove make his peace with the epic public mendacity his case required? What happened to turn the Labour heartlands to Ukip?

The first three questions are fascinating at the level of character; the Brexit decision was so significant, and the human flaws and vanities that created the moment so petty, that it is impossible not to get drawn in. Yet that final question about Labour heartlands – a well-worn euphemism for “deprived north” – is everything. Already an orthodoxy and inevitability have shaped around it: if you take what was traditionally red, add a bolt of blue in the form of defensive nationalism, then of course you get purple – it has the solidity of a physical law.

How history judges Cameron – between hapless victim and appalling bungler – will not have a huge impact on our political landscape; the verdict on Gove, even less. There will be some lasting effect on Labour’s truths and confidence from an analysis of Corbyn, but we can’t hang anything off his performance during the referendum until we accept that both sides are right: he was beset by a hostile media and he was ambivalent.

This story about the deprived north, however, will have lasting and profoundly misleading consequences for the political landscape, if we don’t think more deeply about it.

The prevailing assumption is that the vote was one in the eye for metropolitan elites, and that the white working classes, the disenfranchised and unheeded, the voters hidden on estates, had finally given a message to the Westminster bubble that knew nothing and cared less about their concerns. In fact, most leave voters were in the south: the south-east, south-west – indeed the entire south apart from London voted leave.

They did so by slightly smaller margins – though it is interesting to note that Wales, apparently the hotbed of a self-sabotaging leave movement, driven by a deprivation that only the EU was interested in alleviating, voted out by a smaller margin than the south-west. Yet southerners voted in greater numbers; their votes were decisive. Furthermore, most leave voters are middle class, or at least were of the generation whose housing and pension windfalls put them squarely in the category of wealth.

Analysing voting data by education – where the more degrees you had, the more likely you were to want to remain – is misleading: it was much less common, before Tony Blair’s 1999 pledge to provide tertiary education for 50% of the nation, to go to university, and a degree was by no means a prerequisite for membership of the middle classes.

The more enlightening figures are those that plot voting against housing; yes, social and council tenants voted leave, but so did those who owned their houses outright, the people we might describe as society’s winners. By housing type, the only groups where remain prevailed were private renters and people with mortgages.

In other words, the very most we can say is that leave had some popularity with the disaffected and the disenfranchised; but it was not limited to that group, and the people who swung the vote were affluent, older southerners. Instead, we’ve taken it as a kicking-off point that the Brexit vote was won by a council estate in Bolton.

The result is, firstly, the othering of the north: people think differently up there, and nobody in London could possibly understand them. In the media and, to a lesser degree, parliament, this has turned into a performative defeatism belied by competitive authenticity: you’re more metropolitan elite than me, because I’ve done some polling in Rochdale; ah, but my grandmother is northern and I met someone once from Wirral South, and I can tell you, on the contrary, that you’re the one who will never understand.

Perhaps defeatism from the elite sounds like a good thing, not a moment too soon; except it carries an attendant assumption that poverty has an immovable set of opinions, which cannot be shifted and which it is disrespectful of the wealthy even to name, let alone discuss. Because we wouldn’t understand.

For every one person who voted leave because the global rat race had left them behind, there was more than one person pretty well served by the economy, who voted leave because they believed the line about sovereignty, or because they were still huffy about the European directive on clean beaches, or because they simply associated the EU with faceless change and preferred things to stay the same. The picture cannot be drawn in simple, binary lines between rich and poor. The divisions are, like the crosscurrents in a family, much more layered; and, like a family, insoluble without the presumption of a fundamental ability and ardent desire to accommodate one another.

Secondly, of course, it has become the immigration election, despite the fact that only a third of leave voters cited borders as their chief concern. And this brings with it a host of assumptions that we might loosely class as swallowing Nigel Farage whole: that people who oppose free movement will always oppose it; that it is pointless explaining the lump of labour fallacy, because that is yet more elitist sneering; that public services are under pressure because of foreigners rather than underfunding; that housing is expensive because of demand rather than rent extraction by a capital class empowered by inequality; that the voters have spoken, and now our humanitarian duties to refugees must come second, to the point that we don’t even mention them; that the metropolitan elite must simply accept that it let immigration get out of control and must pay the price of a mistrust of unknowable proportions and unguessable length.

Remaking this picture, so that it resembles reality rather than regurgitates false absolutes, is far more important than any discussion about a second referendum, or a snap election, or a progressive alliance. It is more important even than the terms under which we exit the EU, if indeed we meaningfully do. At stake is our ability to cohere. For the sake of national unity, we must question, rather than merely accept, the new nationalism.