Do you remember where you were when you found out the UK had voted to leave the European Union? I was lying on a camp bed, temporarily installed in a meeting room in 10 Downing Street.

I heard the voice of David Cameron, who would shortly resign as prime minister. He was outside the door, sombrely telling someone on his mobile that it was “going to be a long night”.

He was at least right about that. Examined with the benefit of more than a year’s hindsight, that night feels just as long – as epochal – as it did at the time. Politically and personally.

That morning, Downing Street was Ground Zero in the explosion of an economic and political order that had lasted decades.

And I had my own unpleasant sensation: that the terms of my citizenship had been altered without my consent.

Even more surreal was that I had been helping to co-ordinate the civil service’s communications effort in the run-up to the referendum – until the beginning of the final pre-election “purdah” period, when official government support stopped.

My job was to ensure the Whitehall press team, including our own in Downing Street, successfully executed a media campaign to support a Remain vote.

Consequences for Ireland I felt like a character in a bad movie. A crude device placed in the script to foreshadow a major event. I personified why it was difficult to explain Brexit’s Ireland’s problem: it was as difficult as explaining myself and the place I come from.

I am Irish, and hold citizenship accordingly. I am also Northern Irish – though that complements rather than lessens my primary identity.

And while I will never feel British the way an Orangeman does, I have lived and worked almost entirely in the UK.

It is, in a complicated way, my country too. I felt admiration and affection for a place mature enough to have people like me working at the centre of its government.

I travelled on an Irish passport to do British prime ministerial business. No one batted an eyelid.

That accommodated complexity was underpinned by the common membership of a European political union by two states that had once been one state, and had spent much of the previous century contentiously working out their relationship with one another.

And that, as you know, is to put it mildly.

Coming from Northern Ireland, the shared problem of both these states, a place where we are still fighting the Williamite War of the 17th century – which was of course a pan-European conflict – I understood the theory that the EU had underpinned our peace.

Now I was getting a lesson in the practice.

Being removed forcibly from a broader European context was dismaying. Not because I idolised Jean Claude Juncker or kept framed judgments of the European Court next to my bed. Because I felt instinctively that Europe had something to do with accommodating people like me. And much more importantly, part of accommodating the troubled place I came from.

This instinct was not shared by a majority of UK voters.

That morning in Downing Street, I felt a need to assert my difference, my Irish and my European citizenship, in response to the assertion of difference and nationality by English voters. I was almost caustic when talking to my English colleagues.

Nations. Borders. Identity.

“I fear those big words,” says Stephen Daedalus in Ulysses, “which make us so unhappy”.

The referendum result was – at least in part – a statement of singular Britishness asserted in opposition to smudged, compromised or multifaceted identities.

That was entirely legitimate – and probably predictable – given the simplistic nature of the question posed to an electorate that is more than 80 per cent English.

England has always been used as a synecdoche for the UK – a component part conflated with the whole. The referendum made explicit that this was a political reality, not just a misnomer favoured by American tourists.

Devalued sterling I would stake a lot of devalued sterling on the theory that most voters who commonly say “England” to mean the “United Kingdom” voted to leave the EU.

I do not intend that to sound sneering, but rather to say that this idea of the United Kingdom – as essentially English – is fundamentally in tension with the idea that underpins the 1998 Belfast Agreement, and the broader devolution settlement within the UK.

This was why, as the referendum went on, I became more repetitive to my colleagues.

Vote Leave had virtually nothing to say on Ireland or the Border, but sustained no identifiable damage to their cause as a result. They were assisted by two things.

First, Theresa Villiers. The serving Northern Ireland secretary’s imprimatur offered legitimacy to Leave’s lack of a policy, and prevented both the British government (and probably also the Irish Government) from attacking their position with the zeal they might otherwise have done.

Second, the Remain campaign was based on focusing swing voters’ minds on a narrow proposition: that a vote to leave the European Union was too economically risky. That approach had worked in the 2014 Scottish referendum and the 2015 UK general election.

That strategy was also a rational response to polling data. English voters were going to win or lose the 2016 referendum.

They would likely be asked to vote to leave based on a hot-blooded appeal to raw nationhood. The best antidote to that was a cold-blooded appeal to economic interest.

My colleagues on Cameron’s political team were certainly sympathetic – many of them were also angry about Leave’s approach to the Irish question – but the truth was that not enough target voters cared enough to make it a central campaign issue.

And there wasn’t enough time to make them care.

Ending conflict My own blood affected my judgment. I wanted to explain to people what I felt: it wasn’t true that the EU had nothing to do with ending conflict.

EU commissioners didn’t negotiate the Belfast Agreement, but British and Irish politicians and ministers were better placed to negotiate it because the two countries had moved beyond post-colonial angst to work together as member states.

On the relatively rare occasions during the campaign when Northern Ireland strayed into the Brexit headlines – such as when Tony Blair and John Major visited Derry – it was dismissed by the Leave side as scaremongering about a return to the Troubles.

An easy caricature.

As with Cameron being accused of promising World War Three when he dared to state that the EU was positive for security on the continent.

What has happened since? Northern Ireland has not descended into open conflict, but no one seriously suggested it would.

Our always-fragile devolved Government has collapsed alongside with the limited measure of trust that existed between its two dominant parties.

The death of Martin McGuinness, a boondoggle involving boilers, Arlene Foster saying something crass about crocodiles. They all contributed to the institutions falling apart.

Would any of them have been fatal if the atmosphere of Brexit had not made the poisons work quicker?

It must be remembered that neither Sinn Féin nor the DUP truly believe in a settlement based on multiple identities or pooled sovereignty – the kind facilitated by EU membership.

Both now want to achieve something from Brexit that is less of a compromise than what existed before.

Northern Ireland firmly locked in A harder, more sovereign UK with Northern Ireland firmly locked in, whatever the feelings of those in the North who treasure common citizenship with the rest of their island.

Or a lunge towards Irish unity via whatever means is quickest, and regardless of the feelings of the majority who want to remain in the United Kingdom.

The Irish and British governments now struggle to adjudicate these factions alongside one another.

Northern Ireland, and the whole island of Ireland, is skin in a bigger game between the EU 27 and the United Kingdom. Ireland was barely talked about before the referendum, but its history and people are now at the centre of a bigger European dispute. Not for the first time.

I stayed on in Downing Street for more than a year after the referendum, working in the same job, but with an entirely opposite purpose – to communicate Brexit.But I still don’t know the best way of answering the Irish questions Brexit poses.

Such as how to avoid the presence of customs checks while having separate customs policies North and South of the Border.

Or what happens when one group asserts an identity that others cannot share. It’s best to avoid to finding out.

Perhaps I know this because of where I come from. My hometown of Downpatrick valued sharing in a way that is rare in Northern Ireland.

Political extremes were frowned on. Catholics played cricket; Protestants played Gaelic Football – not many, but a few, and enough for it to matter.

And St Patrick, symbol of Ireland spiritual and temporal, lies buried under a Protestant cathedral.

I grew up distrusting assertions of identity so loud they frighten others.

Those big words, they make us so unhappy.