In the wake of the UK's vote to withdraw from the European Union - a move with profound consequences for the island of Ireland, and for the government in the Republic - relations could take a turn for the worse. The UK accounts for one-seventh of Ireland's exports, and over a quarter of its imports - all of which could now be subject to tariffs.

Perhaps more damagingly, because of fears over inward migration to the UK, border checks between the Republic and Northern Ireland could return for the first time since the end of the paramilitary campaign in the 1990s.

"My first interest is Ireland's interests, namely, the protection of the common travel area, the peace process, the open border we have with Northern Ireland and the future of Northern Ireland citizens," Taoiseach (prime minister) Enda Kenny said in the wake of the vote.

The border between the Republic and Northern Ireland was never quite watertight. Despite constant Army presences during the 30-year armed conflict, the border remained a porous channel for illegal arms and explosives smuggling. But in peacetime, with checkpoints dismantled, the only sign of a border are the signs reminding motorists of how the speed limit switches between Irish kilometers and British miles.

A united Ireland?

The vote has, however, added fresh initiative to calls from the likes of Sinn Féin for the two Irish jurisdictions to be reunited after 95 years apart. While the majority of UK voters opted to leave the EU, in Northern Ireland a majority (56 percent) wanted to remain.

"The British decision puts at risk the human rights legislation that underpins much of the [Good Friday] Agreement, the cross-border bodies and the all-Ireland structures," according to Sinn Féin President Gerry Adams. His party colleague, Northern Ireland's deputy first minister Martin McGuinness, summarizes Brexit simply as a "disaster." Both claim Westminster has now ceded the right to represent Northern Ireland at a global level.

Their calls for a poll on reuniting Ireland have been rebuffed by governments in Dublin and London, who see it as a distraction Northern Ireland could do without. After two decades of work trying to nurture a grey area between deeper shades of green and orange, they fear a referendum would simply entrench and reinforce the previous sectarian divides, forcing moderates to settle on one side or another.

In the meantime, although Brexit will not take effect until 2019 at the earliest, the decision has taken a toll on Anglo-Irish trade. The post-Brexit currency shocks meant Irish exports became 10 percent more expensive to British buyers overnight. Officials also fear an impact for Ireland's pivotal tourism industry - and that British tourists (41 percent of all Ireland's visitors) may now see Ireland as too expensive. "That is a serious prospect for us and something we must recognize," Tourism Minister Shane Ross told a parliamentary committee last week. "The success story will end if Brexit has the worst effects on tourism that we fear."

One former diplomat told DW that the European Council negotiating table often resembled a high school cafeteria, with like-minded groups of states (Benelux, Baltic, Iberian, Nordic) tending to club together. Ireland and the UK were similarly close at a European level, he said; now Ireland finds its closest pal is moving away, and at a loose end when it comes to finding new friends - potentially, perhaps, hoping that its Celtic cousins in Scotland might soon be returning to the table.

New opportunities

There are other unintended consequences from post-Brexit border checks. In recent years the Republic and Northern Ireland have begun to integrate their health systems; a flagship new children's hospital in Dublin is intended to serve the entire island, partly on the basis of subsidies from Belfast.

For this reason, health minister Simon Harris says it’s "absolutely essential" that the common travel area is retained - so that "some of the sickest children in this country" can be treated on the basis of need, not nationality. "Cross-border health is very much the crux of what happens in both our health services on a daily basis, and must continue."

That is not to say the crisis does not open opportunities too. The very morning after the Brexit vote, the Irish Government published a document of contingency plans - among them, the promise to step up Ireland's foreign marketing, chasing "companies who wish to be based in an EU member state." Ireland prides itself on its young, English-speaking, highly educated workforce with an open door to Europe - and is uniquely positioned to exploit any business exodus from London.

"Multi-cultural start ups with 10 or more staff are telling us that they are actively seeking to move their operations to an alternative EU city such as Dublin," Miceál O'Kane, chief executive of recruitment site JobsEngine.com, told DW. "They are telling us that they want to move before the bankers relocate and push up prices."

On the shopping streets of Dublin, however, those concerns take second place to more human fears: fears of a hard border and revived sectarian divides in the North, or that relatives living in Britain could find themselves without residency rights when the UK-EU divorce is finally completed.

"My son moved his whole family to Manchester four years ago for a job," one woman told DW. "It's only an hour away on a plane, and we see them regularly, but that's their home now. And it would kill them if they were told now they couldn't live there, just because they're not English."

"I just don't want anything that might send the North back to the old days and the killing," says another. "We've come too far down that road to turn around and start building walls again."