In my lifetime – and I’ve been observing politics in Northern Ireland for almost 40 years – I can’t remember a moment when Irish unity was so high on the agenda. Sinn Féin is seizing the unexpected political and electoral “moment” provided by Brexit; while the Irish Government, facing potentially huge problems in the event of a hard border, could be considering unity as a possible long-term solution (maybe even with tacit British approval).

Crucially, though, some unionists are also beginning to take the issue seriously. In an interview with Patrick Kielty, about the 20th anniversary of the Belfast Agreement, Arlene Foster was asked about Irish unity. While saying it was all “very hypothetical”, she still gave a serious and important answer: “If it were to happen I’m not sure that I would be able to continue to live here, I would feel so strongly about it. I would probably have to move.”

Ten years ago, maybe even five, no unionist leader would have answered the question, let alone given that answer. But Foster knows, as do many within the leadership of the Protestant/unionist/loyalist/orange communities, that the dynamics have shifted. The once-unthinkable needs to be thought about.

Brexit means there has never been a better time: never been a moment when small-u unionists and small-n nationalists may be prepared to listen to a serious, coherent, pro-unity argument

Meanwhile, for all their talking-up of the “inevitability of reunification” Sinn Féin had long accepted that there was, in fact, nothing inevitable about it at all. That’s why the promise of a Border poll (albeit with no specified time scale and left to the discretion of the secretary of state) was included in the agreement. It gave Sinn Féin something to sell to their grassroots, allowing Gerry Adams to say: ‘The agreement is, therefore, not a settlement, but is a basis for advancement. It marks the beginning of a transitional period towards Irish reunification . . . It will never be enough to say that the nationalist nightmare has ended when it quite clearly has not.’

Border poll

That’s why Sinn Féin needs to get a Border poll as soon as possible. Brexit means that there has never been a better time: never been a moment when small-u unionists and small-n nationalists (the essential demographic that SF needs to win over) may be prepared to listen to a serious, coherent, pro-unity argument. They also need to persuade the Irish Government to start singing from the same song sheet, because Sinn Féin is canny enough to know that they cannot win unity on their own.

DUP leader Arlene Foster: knows the dynamics have shifted in the North. Photograph: Yui Mok/PA

This is, possibly, the most important moment in modern Sinn Féin’s – post 1970 – history: if they can’t secure a Border poll in the next five years, secure endorsement for unity from the Irish Government (and opposition parties) and actually deliver what they’ve been talking about for 50 years (and one of the primary reasons they gave the nod of approval to the Belfast Agreement), then it will be at least another generation before another “moment” comes.

Get it wrong now and they’ll find it increasingly difficult to galvanise support and expand the existing base. Electoral success is built on the electorate’s (that includes non-voters) perception of your ability to deliver your ultimate goal. Perception has favoured them since about 2003, but it will begin to shift.

Most important, they need the Assembly and Executive up and running again; for it is those institutions which have the power to reassure the shaken and wavering

There is a tendency within unionism to do three things when it senses pressure: circle the wagons; talk tough; then hope that the problem just disappears. But they need to embrace the unity debate. They need to ask the sort of questions to which, so far, Sinn Féin hasn’t come up with answers. Yes, Brexit has presented huge and new challenges for the union and that’s even before we know what the final settlement will look like. It has spooked those small-u, small-n voters. It has raised difficult questions about how Northern Ireland will fare in a UK outside the EU.

Relationship with Republic

But it has also presented an opportunity for unionism and unionists to rethink their identity and role in what is going to be a very different era. So they need to set out how they will co-operate with the Republic in this new era. They need to spell out how they will settle the nerves of those who are genuinely unsettled by Brexit. They need to work with the UK government and copper-fasten the precise nature of the relationship with the Republic. Most important, they need the Assembly and Executive up and running again; for it is those institutions which have the power to reassure the shaken and wavering.

Leo Varadkar is openly gay. Same-sex marriage is legal. Abortion laws are likely to be liberalised in a few weeks. There is stable government and genuine choice at elections. Political debate is not dominated by stale, us-and-them squabbles. Equality is one of the cornerstones of society. You can buy drink on Good Friday. Ironically, if there was a Border poll anytime soon, and people compared the lifestyle in the Republic with that in the North, it might be those issues which could swing it away from the union rather than simply membership of the EU.

For so long as Northern Ireland looks like a “place apart” on a raft of key sociomoral issues then for so long will unionists struggle to convince others – as well as some who should be their natural supporters – that they are serious about equality of citizenship for everyone. A unionism which isn’t inclusive, embracing and equality-focused is a unionism with a limited shelf-life.

Alex Kane is a commentator based in Belfast. He was formerly director of communications for the Ulster Unionist Party