Control and consent are intimately related. Where consent exists and is freely given, statements of control are unnecessary.

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The government is determined to deliver on Vote Leave’s promise to “take back control” – to assert sovereignty on behalf of leave voters. But the complicated consent structures of the UK’s most complicated corner, Northern Ireland, are once again getting in the way. On the evidence of the prime minister’s letter to Donald Tusk on Monday, the government is not minded to let that stop them.

This perhaps should not come as a surprise. In one of his blogposts railing against Theresa May’s approach to Brexit negotiations, Dominic Cummings said the last administration had “aided and abetted bullshit invented by Irish nationalists and remain campaigners that the Belfast agreement prevents reasonable customs checks on trade between Northern Ireland and the Republic. It does no such thing.” The senior Brexit strategist went on to describe arguments about the complexity of the Irish question as “babble”. He may not like the rest of this article.

“Be advised, my passport’s green. No glass of ours was ever raised to toast the Queen.” So wrote Seamus Heaney 50 years ago. It remains the most famous statement of sullen Irish nationalist alienation from the British state. But it is also a historical artefact, because in 2011, Heaney did exactly that. He raised a glass to toast Queen Elizabeth while sitting between the Duke of Edinburgh and David Cameron at a state dinner in her honour at Dublin Castle.

What changed? After the squalor of the Troubles and the decades of political turmoil, Northern Ireland found a structure capable – for a while at least – of accommodating its contradictions. That structure was the Good Friday agreement, which was itself contradictory in that it was designed to enshrine the consent of two groups with opposing aspirations. Unionists were reassured that Northern Ireland would remain in the United Kingdom until a majority voted otherwise. Dublin would remove its territorial claim on Northern Ireland and acknowledge UK sovereignty – but with Irish consultation written into the governance of the place.

Facebook Twitter Pinterest ‘Boris Johnson’s letter to Donald Tusk requests the complete removal of the backstop.’ Photograph: Toby Melville/Reuters

Nationalists, whose alienation was in large measure derived from the fact that their consent was never asked for in either the partition of Ireland or the character of Northern Ireland, were given a guaranteed stake in the government via power sharing. The agreement also contained a specific route to future Irish unity via a border poll and permanent citizenship rights – the right to identify as British, Irish or both.

It was, on several levels, a loss of control. But it was rewarded with a strengthening of consent. In a small way, I was an example. I wouldn’t describe myself as a nationalist (or unionist), but I am certainly Irish and carry a passport accordingly – and did so when working for two different prime ministers. I had a British one, too. I didn’t feel British in a conventional way, but I certainly felt huge respect for the way the British state was able to accommodate people like me.

I left the government a while ago now, in part because the contradictions involved – at least in Brexit policy – became too stark. For many moderates in Northern Ireland, accepting contradiction has not just been about pragmatism, but ethical choice in the context of a divided society and grim history.

By loosening its control of Northern Ireland, the UK solidified the consent of people there for the status quo. Quite an achievement, but one which seems to belong to a different political age, which of course it does. In his letter to Tusk requesting the complete removal of the backstop, Boris Johnson correctly says that the Good Friday agreement and broader settlement are founded on a “delicate balance” between two traditions and the principle of consent. But in asserting hard UK sovereignty in Northern Ireland – as the letter also does – the government is at risk of undermining the hard-won consent of people who do not rally to the flag in the unambiguous way of the Tories’ Democratic Unionist partners.

Most intriguingly, the letter argues that the Good Friday agreement is founded on the protection of “minority rights”. This is a phrase that never appears in the agreement. It implies a decades-old view of Northern Ireland being constructed of a unionist majority and nationalist minority. This is simply no longer true. Unionist parties have not won a majority of votes cast in a Northern Ireland election since 2005. While there is likely still a majority for Northern Ireland remaining in the United Kingdom, this is not the same thing as a “unionist majority”. Both unionism and nationalism are minorities now, with the balance being held by an unaligned, liberal middle.

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Where there is a majority is for the backstop. Successive polls and the European election results indicate nearly 60% consistently voting in favour of special arrangements to accommodate Northern Ireland’s strangeness. We have come to quite the historical pass when a government in Dublin finds itself pointing out that the will of the majority of partitioned Northern Ireland should be respected. Wherever Éamon de Valera and Edward Carson are now, we can only hope they are able to enjoy the irony together.

Another irony: that less control can mean more consent seems tragically to have been forgotten, at least in London.

• Matthew O’Toole is a former No 10 Brexit spokesperson