DUBLIN (Reuters) - When Britain voted to leave the European Union, few voters outside Northern Ireland thought about what it would mean for the British province.

Former SDLP leader Mark Durkan, now running as a Fine Gael candidate contesting the Dublin constituency for the European Parliament elections, canvasses for votes in Dublin, Ireland, May 20, 2019. Picture taken May 20, 2019. REUTERS/Clodagh Kilcoyne

Three years on, Northern Ireland is inching closer to holding a referendum of its own -- on reunification with Ireland.

A united Ireland, and Northern Ireland’s withdrawal from the United Kingdom, remain distant prospects, and a unity referendum may not happen soon. But, as an unexpected consequence of Brexit, the political landscape is shifting.

The two largest parties in the Irish republic, Fine Gael and Fianna Fail, both of whom ultimately favor a united Ireland, have expanded their political networks north of the border to position themselves for a possible “unity vote”.

Fine Gael, Ireland’s governing party, has also taken the unusual step of selecting one-time Northern Ireland Deputy First Minister Mark Durkan as a candidate to run in the Dublin constituency in this week’s European elections.

“The unity debate has gained legs in the context of Brexit,” Durkan, a former leader of the Social Democratic and Labour Party (SDLP), one of Northern Ireland’s two main pro-unity parties, told Reuters while campaigning in the Irish capital.

In the 2016 Brexit referendum, nearly 56% of voters in Northern Ireland voted to stay in the EU but the province will leave when the rest as Britain departs -- on a date that has not yet been set. Ireland, which won independence from Britain a century ago and joined the EU in 1973, will remain in the bloc as its most committed member, according to recent polling.

Opinion polls in Northern Ireland have for many years shown insufficient support for reunification, but politicians and political analysts point to a growing number of factors that could push public sentiment in the direction of reunification.

The first is the possibility that Brexit will lead to a “hard border” between Northern Ireland and Ireland, meaning the re-emergence of checks on goods and a potential a risk to two decades of delicate peace in the province -- a prospect that alarms many people both north and south of the border.

Another is the economic and political situation. Recent business surveys suggest that despite record low unemployment, Northern Ireland’s economy is stalling, partly because of uncertainty over Brexit. The province’s devolved government, created under a power-sharing agreement in 1998, collapsed more than two years ago.

Demographic trends could also shift public opinion in favor of unity. Catholics, the traditional support base of Irish nationalist parties and unity, are on course to become the majority in Northern Ireland within a generation.

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This would be important because of the terms of the 1998 Good Friday Agreement, which ended decades of sectarian violence over whether Northern Ireland should remain British or join the Irish Republic.

The agreement specifies that the British government “shall” order a referendum on whether Northern should remain part of the United Kingdom if it appears likely that a majority of those voting would seek to join a united Ireland.

PREPARATIONS FOR A UNITY VOTE

Anxious not to be caught unprepared if there is a unity vote, Fine Gael has extended its reach north of the border by opening a youth branch in Queens University in the Northern Irish capital, Belfast.

Its invitation to Durkan is intended by Prime Minister Leo Varadkar so show Fine Gael is prepared to help Northern Ireland have a voice in the EU assembly once Brexit forces the representatives Northern Irish voters will elect this week to give up their seats.

Fianna Fail, Ireland’s biggest opposition party, has more directly courted the SDLP and their voters by signing a cooperation pact with it earlier this year.

The moves reverse a long-standing policy under which the two dominant political forces south of the border have avoided direct participation in politics north of the border because of fears that the nationalist vote could be fragmented.

“The Fianna Fail policy partnership with the SDLP is one response to some of the challenges that Brexit raises,” Durkan, 58, said.

Explaining that he saw no competition between the approaches to SDLP voters from two different Irish parties, he said: “Fine Gael’s invitation to me is a different, but not rival, response.”

Northern Ireland’s largest Irish nationalist party, Sinn Fein, which is also the only major party represented in the parliaments in Belfast and Dublin, is already demanding a referendum on Irish reunification, echoing calls by the Scottish National Party for another referendum on Scotland’s independence from the United Kingdom following Brexit.

Fine Gael and Fianna Fail have not called for a unity vote anytime soon.

“We need to concentrate on the Brexit challenge first and we need to get the institutions of the Good Friday Agreement back and fully restored,” Durkan, one of the architects of the 1998 peace accord, said.

With Northern Irish unionists - supporters of staying in the United Kingdom - worried they could be forced to become part of Ireland simply because Protestants will one day be outnumbered, Fine Gael and Fianna Fail are moving cautiously because they realize reunification would be difficult if their appeal did not go beyond nationalist voters.

“It would blight this Ireland for 75 years if you just based this on demographics alone,” said Trevor Ringland, a Belfast-based unionist known on both sides of the border after playing rugby for Ireland, one of the few sports that draws on players from both jurisdictions to field one national team.

“The alternative is work together, build relationships and if future generations want to change the constitutional position then let them do it in a place that is succeeding,” he said, referring to the need to make devolved government work first.

LOOKING FOR “SOMETHING DIFFERENT”

For Jude Perry, a 20-year-old student who set up the Young Fine Gael branch in Queens University, once a symbol of the Protestant establishment’s dominant position in Northern Irish society, the expansion into Northern Ireland is the beginning of a new phase in all-island politics.

It also follows local council elections this month that signaled there is some appetite for change. While Sinn Fein and the Democratic Unionist Party (DUP) retained their dominant position, the still small cross-community Alliance Party made by far the biggest gains.

Its leader is also in contention to win the party’s first European parliamentary seat this week.

“There are a lot of young people looking for something different, something middle ground,” said Perry.

“I don’t think people are as tribal as we make them out to be. There is more to politics in Northern Ireland than flags and lampposts.”