It’s important not to romanticise the past, otherwise you end up like a cut-price, leftist Nigel Farage marching to a whinier, less exhilarating drumbeat. But I distinctly remember, this time 20 years ago, it being normal to object to Halloween: not because it was satanic, but because it was American. It was the festival of consumerism and excess, unmoored from any deeper significance, but most of all – being expressly conceived as fun for children, and entailing talking to strangers and asking for things – it was un-English.

Nationalism has taken a depressing turn, this past year and a half. The suspicion of foreigners and alienation of former allies are the greatest practical threats to the country’s wellbeing and prosperity. The let-Britain-roar, grow-wings-and-fly pap is the most unsettling departure from maturity and reason. But it’s the exceptionalism, freely vented for the world to hear, that is the most embarrassing: the idea that our success is assured, whatever decisions we make, because we’re the best at trading, with the best stuff, the finest minds, the most illustrious history. It’s the delusional boastfulness of sketch comedy, a parent standing in a playgroup yelling at everyone to agree that their child is the most advanced.

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This is not, however, a story of a nation that was bumbling happily along when suddenly the patriotic beast within was awakened. There was no shortage of national identity before it mutated and was weaponised. There was a very clear sense of Englishness. It was just a different England.

Prior to this Tory rampage, we didn’t say “British”, because we all knew that was a euphemism for “English”, which itself was code for flag-toting, nostalgic monoculturalism. But we were pretty comfortable describing what was un-English: self-aggrandisement; vocal pride – especially for things you had no hand in, such as where you were born; and making large claims for superiority in abstract areas, like national character. These were un-English. The idea of “British values” was oxymoronic, since appropriating some value and claiming to have it in greater quantity than any other country would have been the least English thing.

Of course, you cannot claim for yourself the accolade “most modest”, unless you’re Donald Trump. So the foundation stone of this patriotism was pride in the thing you wouldn’t be seen dead taking pride in: or, to put it more briefly, all nationalism was ironic. We used the union flag ironically, as a backdrop for Patsy Kensit or to set off Liam Gallagher’s eyes. We mentioned national traits only to mock them – chiefly, a collective inability ever to say what we meant. Irony, at the turn of this century, became synonymous with insincerity: a thin gruel, no match for the hearty stew of passion.

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But in fact the irony was anything but insincere. Rather, it was the navigational tool of acute self-awareness, an acknowledgment of a delicate tightrope between celebrating the achievements of your compatriots and lauding them as proof of your nation’s supremacy; between feeling loyalty to your fellow citizens, in recognition of the fact that you were all embarked on the creation of a shared future, and fostering an us-against-the-world interiority; between relishing cultural cross-pollination and importing any old nonsense, like Halloween.

A nationalism constantly asserted defines itself against the foreign; a nationalism that goes unstated defines itself from within – its tacit understandings are its connective tissue. It was no accident that we rarely talked about patriotism. But if meaningful patriotism is social – a nationhood based on building collectively within borders, not for geographical reasons but because those are the perimeters of your democratic agency – there was never any shortage of it.

Subtlety has its drawbacks. That brand of tacit solidarity has been under attack now since 2010, when it became routine to divide citizens by whether or not they claimed benefits, were hard-working, were economically active, were northern or southern, were net contributors or recipients. It would have been good to rebut these tropes and defend our sense of responsibility for one another a bit more vocally, rather than leaving it to Twitter and The News Quiz. But ironic distance, the instinctive distrust of grand passions hurled bombastically about, was also protective. It would have been impossible, when irony was the signature of national identity, to imagine a prime minister speechifying about “taking back control” when she didn’t have control even of her three nearest underlings. It would have been unthinkable for ministers to talk about importing chlorinated chicken or growing our own food as an alternative to being party to modern international trading agreements. Not because we would have laughed – we’re laughing now – but because they would have anticipated the ridicule and taken some rudimentary steps to avoid it.

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A politics with no sense of the absurd starts to believe its own flourish. Without the deflation of humour, the government is locked into an ever-building climax of preposterous overstatement and bald assertion. Its decisions have never been more consequential, and their unfolding never more dramatic. Yet every week feels eerily similar, ominously stalled. Following Brexit is like trying to find your way out of the woods in twilight and seeing the same tree again and again. It’s gone from disaster movie to horror film: the May Witch Project.

I am reconciled to the import of Halloween. Tomorrow I will dress as a Person With Nits, exactly like a regular person, except with nits, and my trick will be to stand really close to people. I cannot, however, reconcile myself to this post-English politics, pumped-up, self-regarding and humourless. If our national identity meant anything, Brexit is its opposite.

• Zoe Williams is a Guardian columnist