There are fears the UK will end up with a ICE-style immigration system

The rise of Nigel Farage has prompted political leaders across Ireland, Northern Ireland, Scotland and Wales to confront a scenario that until recently was considered highly unlikely, the possible breakup of the United Kingdom.

Supporters of the Union and advocates of Irish reunification alike are preparing for uncertainty should Reform UK take a large step at the next general election, either by putting Mr Farage into Downing Street or by establishing the party as the official opposition.

Politicians on both sides believe a Reform-led government could rush calls for a referendum on Irish unity while pursuing tougher immigration policies that would cause unrest among the nations.

Even the prospect of Reform holding significant power in opposition or as part of a coalition has prompted fresh concern.

Mark Drakeford, the former First Minister of Wales, warned that the political landscape could shift rapidly if Reform continues its rise.

“It is conceivable that in just a handful of years’ time, people on the island of Ireland will be looking across the Irish Sea to a country where ICE-like snatch squads are arresting people off the streets.”

Although Mr Drakeford has consistently argued for preserving the Union, he believes British politics has undergone a fundamental change and fears “there may not be time” for a measured debate on the UK's future if Reform expands its parliamentary presence.

He continued: “The United Kingdom is a voluntary association of four nations, and in any voluntary association there must be choices that people can make to stay in and choices that people can make to leave.”

His comments came during a conference in Belfast organised by the Social Democratic and Labour Party (SDLP), where politicians from across Britain and Ireland discussed the possibility of being "bounced" into constitutional change by events unfolding in Westminster.

Ireland's Justice Minister, Jim O'Callaghan, argued Dublin should begin preparing for reunification rather than allowing English nationalism to dictate the pace of events.

“The future may not go down the predictable pathway of discussions and harmony," he said.

Much of the talks focused on the financial support Northern Ireland receives from Westminster, estimated at between £6billion and £20bn each year.

Several speakers suggested the issue could become a political target for Reform in much the same way Brexit campaigners focused on Britain's financial contribution to the European Union.

“Wait till he sees our bill,” said SDLP leader Claire Hanna. “I think if English nationalists really dive deep into the resources that Northern Ireland requires, that could become a political football, a political problem.”

She argued the lessons of Brexit demonstrated the risks of entering constitutional debates without proper preparation.

“Brexit was a lesson in how not to do constitutional change, and since then British politics had changed in a structural way. We can no longer say the Nigel Farage phenomenon is a flash in the pan, unfortunately. It’s a feature now of UK politics. So it is prudent for us to think about our own constitutional future and not be passengers in wherever politics wishes to take us.”

Sinn Féin has long campaigned for a referendum on Irish reunification, but insists any vote must be preceded by extensive planning and consultation. Under the Good Friday Agreement, the British Government can call a border poll if it believes a majority in Northern Ireland would support joining the Republic.

Conor Murphy, a former Sinn Féin Finance Minister at Stormont who now serves in the Irish Senate, warned against allowing political developments in London to determine the timetable.

“We can’t afford to take chances on what might come next from London.”

Murphy believes the annual financial support provided to Northern Ireland is lower than some estimates suggest but said larger figures could easily become a political weapon.

“He could say: ‘We’re going to save that by letting the Irish go and good luck to you and goodbye.’ He could do that. I’m not suggesting that he will but it’s kind of the nature of their policies. It’s Trump-like. It’s unpredictable.”

Jon Burrows, leader of the Ulster Unionist Party, warned that English nationalism could strengthen support for constitutional change across the UK's devolved nations.

“It could create more fertile ground for those who want to tear apart the United Kingdom.”

Instead, he argued unionists should make a stronger case for Northern Ireland's place within the Union by emphasising its economic contribution and strategic importance.

“I’m increasingly trying to get our message out about what Northern Ireland brings to the union.”

Mr Drakeford said he still hoped the United Kingdom would endure but warned rising English nationalism risked driving Scotland and Northern Ireland away, leaving Wales politically isolated.

He suggested Wales could eventually seek closer cooperation with Scotland and Ireland through a Celtic partnership modelled on the Nordic Council.

He also warned that Reform would not need majority public support to secure power under Britain's electoral system.

“The perversity of the first-past-the-post election system means that you can get a government, as we have now, with a big majority on 34% of the vote.

“From a Welsh point of view, this could lead to the worst of all possible outcomes – not one in which the people of Wales choose to leave the United Kingdom, but in which the United Kingdom has left Wales.”