When the permanent Brexit deal is struck, Northern Ireland will be watching especially closely

When we leave the EU on Friday more than one border will be affected.

Our team in Northern Ireland have been getting a handle on the enormous effect Brexit has had on the balance of public opinion here.

For many of us, it is the most enormous of questions: whether southern and Northern Ireland could ever unite. We thought it had been put to bed by the Good Friday Agreement but after just two days on the border and in Belfast, it appears to be only sleeping.

First up, Carlingford Loch – the ferry between northern Greencastle and southern Greenore - where businesses and day trippers alike travel between the two countries freely.

We spoke to Irish hikers who had been up Northern Ireland’s highest peak, Slieve Donnard, that morning and were already on their way back into the Republic; a business woman and a grandmother who had just picked her daughter up from Dublin airport. All thought Brexit had made a united Ireland more likely. One said she thought it would now happen in her life time; another said that she could see it in the next ten years.

It’s Brexit that has nudged people this way. The withdrawal agreement creating a new border in the Irish Sea between Northern Ireland and the rest of the UK may see intrusive time-consuming border checks. Boris Johnson insists it won’t; Michael Barnier disagrees, so let’s see.

Northern Ireland also does more trade with the rest of the UK than Ireland. If Boris Johnson is right, then perhaps Brexit comes to pass and little changes.

But if it is the case that Northern Ireland comes to feel more economically unified with southern Ireland than it does with Britain, then how long before it follows politically and constitutionally?

The Good Friday Agreement requires the Secretary of State for Northern Ireland – currently Julian Smith – to hold a so-called border poll (a referendum) of both the Irish and the Northern Irish if it looks ‘likely’ that such a poll would be won. (This question of what constitutes ‘likely’ when opinion polling is such a fraught business occupies some of Northern Ireland’s finest constitutional brains as we speak).

This mechanism was put into the Good Friday Agreement to please nationalists but apparently, at the time, many never thought it would ever be used (Gerry Adams had said, in the previous Brexit era that feels like a geological period in the past, that a united Ireland wouldn’t happen in his life time).

But now in Belfast, many are discussing how it might be triggered sooner than expected. Academics and political pundits we spoke to said they thought things were moving fast – the most conservative estimate was that it would be held in the next ten years, possibly in five and one wouldn’t rule out it being sooner than that.

The key thing is going to be the centre ground of Northern Irish public opinion.

There are hard rocks of opinion at either end of the debate – the nationalists who will always want a united Ireland and the unionists who will always want the link with the rest of the United Kingdom. But in between that – the pragmatic centre ground of northern Ireland is growing and, in the words of Alex Kane who was an advisor to David Trimble and former head of communications for the UUP, “persuadable”. He has dedicated his life to keeping Northern Ireland in the UK but now thinks an ‘all Ireland’ could happen.

“There is a demographic called ‘small n nationalist’ small u unionist who are fairly comfortable in the United Kingdom with this multiplicities of identities are protected – by the European union and the link with Britain and the link with Dublin now they fear that identity is under threat… being challenged and people who wouldn’t have considered if you had asked them five years ago, about an united Ireland they would have said not now not now… they are willing to listen to the argument and that is the big change.

Professor Katy Hayward, of Queen’s University Belfast, agrees – if this pragmatic group believe that Brexit has damaged their jobs or local economy, breadline issues, then they will look to the Republic of Ireland.

58% of Northern Ireland voted to Remain in the EU and they could come to see uniting with Ireland as the way back in. If Brexit is a success, the question will wither as the centre ground of Northern Ireland accepts the new arrangement. Remember too that Northern Ireland enjoys the NHS, but the Republic of Ireland has a private health care system where people pay for appointments. Many we spoke to raised that unsolicited as something they would lose, and not like losing, in a united Ireland.

It is not an uncomplicated prospect for the Republic of Ireland. Northern Ireland is the poorest region of the United Kingdom and academics have worked out this cost of ‘on-boarding’ – absorbing Northern Ireland’s economy into the Republic would be considerable.

We’re a way away from that yet. People in Northern Ireland may be reporting thinking a ‘united Ireland’ more likely but it doesn’t mean they necessarily want it in great enough numbers. But when that permanent Brexit deal is struck, northern Ireland will be watching especially closely.