City hall in Belfast UK, the capital of Northern Ireland (Shutterstock)

For Damian McGenity, a farmer in Northern Ireland, Brexit is pushing Irish unity back on the agenda.

"Before Brexit, the only people talking about a united Ireland were politicians; it wasn't on the horizon, but now it's in people's minds," the 44-year-old from Armagh said. "There is no question, Brexit has brought that about."

Fifty-six percent of Northern Ireland voted to remain in the European Union, and now with polls showing rising support for reunification, anti-Brexit forces in the region are calling for a referendum on the issue within five years.

Although chances of such a vote in the foreseeable future are slim, a so-called hard Brexit could change the dynamic. Some 48% favour staying in the EU by joining the rest of Ireland in the event of a hard Brexit versus 45% wanting to stay with the UK, according to a LucidTalk poll in December.

As Brexit talks continue, however, there's little prospect of the UK government agreeing to a referendum, as politicians on both sides of the border say a vote could stir up sectarian tensions. Former Irish prime minister John Bruton this week warned that a border poll could be "deeply destructive."

"There is a persistent and widespread fear among both communities in Northern Ireland that such a push for a United Ireland would cause further political turbulence, sectarian animosity and violence," said Edward Burke, assistant professor in International Relations at Nottingham University, who's researching the effect of Brexit on the British-Irish security relationship.

Northern Ireland remained part of the UK when the rest of Ireland won independence in 1922. The UK and Ireland joined the EU together in 1973 at a time when sectarian violence and tit-for-tat bombings were escalating in Northern Ireland.

Economic dependence

Border controls largely melted away in the 1990s as both economies were part of the single market and the Good Friday Agreement led to a cessation of hostilities between mainly Catholic republicans fighting for a united Ireland and Protestant unionists loyal to the UK.

Northern Ireland voted to stay in the EU mainly because of strong support among Catholics, rather than the Protestants who back parties like the Democratic Unionist Party, according to John Garry, Professor of political behaviour at Queens University in Belfast. Three quarters of DUP voters opted to leave, he said.

Sinn Fein, which represents nationalists who want a united Ireland, campaigned for "remain," and with the region voting to remain in the EU, says the time is coming for a unity poll.

DUP's William Irwin

Photo: AFP

"The Brexit issue, with the denial of the democratic rights of people here, the complete lack of interest or understanding from London as to how an EU exit would impact on the community and the reliance on Dublin to protect the economic interests of the island has accelerated the debate," said Conor Murphy, a member of the region's power-sharing assembly.

Unionists Disagree. The DUP's William Irwin dismisses that.

"The border between the Republic of Ireland and the UK is something that will remain in place for a very long time," said Irwin, 60. "The UK, of which Northern Ireland is an important and integral part, will grow stronger outside the EU."

In some respect, polls back him. Only 34% of Northern Irish voters back Irish reunification, according to a LucidTalk poll in October - a vote can be only be held if Britain judges it likely that the region would back for unity.

There's another fear among unionists -- that Brexit creates a united Ireland, almost by stealth. At present, the only plan on the table for keeping the border invisible is the EU's "backstop," which would effectively keep Northern Ireland in the customs union and parts of the single market.

Unionist Danny Kennedy, 58, doesn't think Brexit will lead to a united Ireland, but could create a "hybrid situation where we are neither British or Irish."

"If there is a border down the Irish sea, Irish nationalists and Republicans will say we have it in everything but constitutional name," he said.