On 24 June 2016, shortly after the Leave victory in the European Union referendum was declared, Anne Walker, a former IRA member, phoned the Warrington Peace Centre in Cheshire in a state of anxiety. The centre had been established to promote reconciliation following the IRA bombing in March 1993 that claimed the lives of two young boys, Tim Parry and Johnathan Ball. Walker was worried that Brexit would cut off EU funding for the centre. “We’ve had a long, long conflict here,” she told me. “We’ve come so far in such a short number of years.”

Walker’s personal story, her association with Warrington and her reaction to the referendum are a reflection of how deeply Ireland will be affected by Brexit, despite the issue’s neglect during the campaign.

The prospect of Britain’s departure from the EU has shaken the fragile structures of the Good Friday (Belfast) Agreement, which was signed in 1998. It has polarised the unionist and nationalist communities. It has left the relationship between Dublin and Northern Ireland’s Democratic Unionist Party (DUP) in tatters and has brought Anglo-Irish relations to their worst point since the early 1990s.

It will also reshape the political dynamics in Ireland, where Sinn Féin is challenging the mainstream parties Fine Gael and Fianna Fáil like never before. “My Irish counterparts were warning about how dangerous Brexit was, right back at the start,” said one senior British official. “We’ve taken it for granted that we all speak the same language. But what this last month in particular has shown us is that it’s all much more fragile. The border is back in Irish politics.”

At the age of 21, in the late 1980s, Walker was part of an IRA “active service” unit, poised to attack a British army patrol in Derry-Londonderry. The attack was thwarted by the security forces. Walker, however, avoided imprisonment because she had suffered a brain haemorrhage as she lay in wait by the roadside that evening.

Walker spent the next years haunted by both her medical trauma and her involvement in the republican movement. The process led her much later to Teya Sepinuck, an avant-garde playwright based in Philadelphia, who had brought her “Theater of Witness” project to Derry-Londonderry in the late 2000s. There, a local drama company was exploring ways to kick-start a truth and reconciliation process. In the US, Sepinuck had brought perpetrators and victims together and, through their encounters, forged harrowing but cathartic stage performances. In Northern Ireland, Sepinuck introduced republican and loyalist activists, Royal Ulster Constabulary (RUC) officers, local councillors and others – bitter foes all.

Walker was paired with Kathleen Gil­lespie, whose husband, Patsy, had been strapped to a van packed with explosives and forced by the IRA to drive it to a British army checkpoint at Coshquin in 1990 (he and five soldiers were killed instantly).

The project was possible only because Sepinuck had secured two grants from PEACE, the EU’s programme to support reconciliation in Northern Ireland and the border region of Ireland, which has paid out more than €1.3bn since 1995.

“I know how many people’s lives were changed by this,” Sepinuck told me by phone from Philadelphia. “The performers, but also the audience. Without the EU money, nothing would have happened. No one would have given us the funding to do this. It was deeply, deeply important.”

Despite the size of the budget, funding for PEACE, which only applies to Northern Ireland, has never been refused by the EU member states. The money is disbursed on the strict condition that it is spent on cross-community projects that foster reconciliation. Unlike the US-backed International Fund for Ireland, the EU money has been considered by loyalists as “neutral” (loyalist ex-prisoners have benefited in particular).

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Europe had long played an offstage role in the Irish conflict. The two parties that dominate Northern Ireland today, Sinn Féin and the DUP, were opposed to EEC membership in the 1970s. In the Irish Republic, Sinn Féin campaigned on the No side in every EU treaty referendum in the 2000s.

Following the election of unionist and nationalist MEPs to the European Parliament in 1979, however, there was a degree of pragmatic co-operation in Brussels and Strasbourg that was painfully absent in Northern Ireland. Indeed, it was the dogged lobbying by cross-community MEPs – John Hume (Social Democratic and Labour Party), Jim Nicholson (Ulster Unionist) and the Reverend Ian Paisley (DUP) – that resulted in the EU’s more direct support, following the IRA and loyalist ceasefires in 1994.

Brexit has shattered that consensus. A survey by John Coakley and John Garry at Queen’s University Belfast found that 85 per cent of Catholics supported Remain, compared with only 40 per cent of Protestants. The DUP found common cause with Leave, while most other parties supported Remain, which secured 56 per cent of the total vote in Northern Ireland. That the result in the whole of the UK was different left a widespread sense of betrayal. It looked as if the British mainland was dragging the province out of the EU against its wishes, and that the careful balance of the Good Friday Agreement was being ignored.

Sinn Féin’s then deputy first minister, Martin McGuinness, responded by calling for a referendum on a united Ireland. A recommendation by the Irish government for an all-island dialogue was slapped down by Arlene Foster, the leader of the DUP. Relations have been in deep freeze since.

The EU’s role was more subtle than merely an injection of cash. The Good Friday Agreement provided room for politics and identity to breathe. A third identity – European – helped that Venn diagram even further. Peter Sheridan, a former assistant chief constable in the Police Service of Northern Ireland (PSNI) and the current chief executive of the peace-building charity Co-operation Ireland, told me: “The context of European integration took much of the heat out of the border issue. After the Good Friday Agreement, you had this idea of a region whose inhabitants could be British, or Irish, or both. Europe made that easier to imagine. You had this new concept of being Northern Irish within the context of Europe. That was particularly true for a lot of northern nationalists who had contested issues of identity. That changed after the referendum, because… now that identity [is] being Northern Irish within the context of the UK. It doesn’t seem to fit as well.”

The irony is that the gestation period for Brexit coincided with a golden age of Anglo-Irish relations. The end of the Troubles allowed mutual ties of family, culture, sport and history to blossom. The state visit of Queen Elizabeth II to the Irish Republic in May 2011 was the crowning moment of this success story. After the Brexit vote, reinforcing that bilateral bond was the obvious first resort. At a hastily arranged visit by the then taoiseach, Enda Kenny, to Downing Street in July 2016 to see Theresa May, there seemed to be a meeting of minds: things should continue the way they were between Ireland and the UK.

“Very clearly from the word go they were saying all the right things,” an Irish diplomat who was present told me. “They were talking up their determination to avoid damaging the peace process, keeping open the border in Ireland – not returning to the borders of the past, as [May] kept saying.”

But as summer ended and autumn began, Irish officials were growing increasingly concerned. Reassurances turned into blandishments. As Boris Johnson, Liam Fox and David Davis jockeyed for pole Brexit position, it led to what Dublin saw as infuriating rank-pulling.

First, Davis’s diary secretary sent an email to the department of the taoiseach asking “if Kenny is available”. A curt note went back to remind Whitehall that the taoiseach’s interlocutor was Theresa May and, second, that you don’t refer to the leader of another country by his surname.

When Davis eventually visited Dublin in September that year, he sought separate meetings with different ministers. Suspecting that he wanted to sow division, the Irish government decided that he would have to meet everyone together in one room. When the British side suggested that the EU would not dare punish the UK because of Brexit, the Irish side bristled, saying that this was an act of self-harm by Britain that would harm Ireland, too.

The Irish government was well aware of the risks that Brexit posed, most significantly to the peace process. But Dublin began to assess other perils. Departure from the EU would affect the Common Travel Area, labour migration, work permits, export controls, military goods, foreign direct investment and various cross-border and state agencies. “Even just namechecking what we were covering took about 20 or 30 pages,” one senior Irish civil servant recalled.

While Ireland had reduced its dependence on the UK, it was still the most important destination for its food exports. In 2016, some 270,000 tonnes of beef worth €2.4bn found its way on to British supermarket shelves. Irish farmers regarded the UK as a high-value market that could not be replaced in continental Europe.

Some regions that depended on these trade flows had little else by way of employment. Along the border, this was particularly acute: producers were dependent on tightly bound cross-border supply chains. Around 800 million litres of milk cross the border each year due to a concentration of processing capacity in the south. Pigs generally travel north for slaughter, while sheep go in the other direction.

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In the autumn of 2016, the triumphalist rhetoric at Theresa May’s first Tory party conference as leader further worried the Irish government. Dublin hoped – and still does – that the UK would remain in the EU customs union and single market, believing this to be the best way to avoid the iniquities of Brexit on the island and on two-way trade. British officials, however, could not give hard answers to Irish questions, and Ireland was being reminded that it would have to declare for the European team.

Writing in the Irish Times in January 2017, Ireland’s European commissioner for agriculture and rural development, Phil Hogan, urged Dublin to step away from London. It would be a “fundamental error” if Ireland placed an “excessive reliance” on its bilateral relationship with the UK as a way to shape its strategic interests. “If we don’t step up to the plate in managing this fundamental shift in our relationship with our European neighbours,” Hogan wrote, “then others will shape the environment for us.”

Yet Dublin still had to manage a fractious three-way relationship with London and Belfast. Forging a consensus was proving impossible. In November 2016, there was a discreet gathering of British, Irish and Northern Irish politicians at Crosby Hall, the splendid Tudor mansion in Chelsea owned by the businessman and chair of Co-operation Ireland, Christopher Moran. The event was ostensibly called to mark the gifting of a portrait of the Queen to Co-operation Ireland by the artist Colin Davidson, but a dinner was also arranged. Present were Martin McGuinness, Arlene Foster, Mike Nesbitt (the then leader of the Ulster Unionist Party), Colum Eastwood of the SDLP, Frances Fitzgerald, Ireland’s then minister for justice, Darragh O’Brien from the opposition Fianna Fáil party, James Brokenshire, the then secretary of state for Northern Ireland, and others. Theresa May was invited, but she was on a trade mission to India.

“It was about finding common ground,” recalled one person who was present. “Brexit is going to happen, but how do we make it in the best interests of everybody? We were aware of the tensions around this. The Irish government were in the unenviable position of being, on the one hand, part of the EU27, but on the other, knowing that their closest neighbour, with whom they do the most trade, is on the other side of the table.”

The meeting was tense, polite and ultimately fruitless. A few weeks later, the Northern Ireland Assembly and executive collapsed over a renewable energy scandal and deepening antagonism between Sinn Féin and the DUP.

This was a grave setback. But Dublin had other concerns. Over the next 12 months, the Irish government embarked on the most bruising and ambitious diplomatic venture in the state’s history. Working closely with the European institutions and other member states, Ireland had to embed its analysis of the impact of Brexit and the solution to minimise it into the European consciousness. The task was made more difficult by Ireland necessarily having to diverge from its close relations with London.

The efforts soon bore fruit. After Theresa May triggered Article 50 in March 2017, the Irish concerns were planted front and centre in the EU’s response, its negotiating guidelines.

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The EU was clear that Ireland was one of three issues on which the UK had to make “sufficient progress” if it wanted to proceed to trade talks. Not only were Ireland and the EU demanding that Britain solve this problem; Dublin had also managed to secure language that, in the event of a successful referendum on a united Ireland in the future, Northern Ireland would automatically be spirited back into the EU.

Dublin’s intent was clear and serious. It was fully backed by Brussels but, according to Irish diplomats, underestimated by London. By the summer of 2017, Enda Kenny had been replaced as taoiseach by Leo Varadkar, who brought a harder edge to Ireland’s posture.

Things came to a head in early November last year. An EU task force paper suggested that the only way to avoid a hard border would be for the rules on both sides of the border to remain the same when it came to the EU single market and customs union. To many, that was akin to Northern Ireland staying in both, while the rest of the UK left.

The British government cried foul; unionists were furious. But May was under pressure to deliver “sufficient progress” on Britain’s financial settlement, the rights of EU citizens and the Irish border before the deadline of 4 December 2017.

Negotiations intensified. Keeping north and south within the same regulatory EU framework would necessitate checks at Northern Irish ports on goods coming in from Great Britain. This would require a border on the Irish Sea, an absolute red line for the DUP, on whose support Theresa May relied for her survival.

By the morning of 4 December, a deal was apparently within reach. All sides would see if a free trade agreement between the EU and UK could realise the objective of having no hard border. If that didn’t work, the UK would propose other solutions, potentially devolving more powers to the Northern Ireland executive. If that failed, there would be “continued regulatory alignment” on both sides of the border.

The deal needed a political sign-off from May and the European Commission president, Jean-Claude Juncker, at a working lunch in Brussels. But when RTÉ News broke the story that London appeared to have conceded the principle of keeping Northern Ireland close to the single market and customs union, the DUP revolted, storming en masse down to the lobby of Stormont in Belfast to denounce the idea. May, still at the lunch, called Arlene Foster. The deal was off.

The collapse was momentous. But May was given another deadline to salvage the agreement. Dublin was not budging on the principle of avoiding a hard border by keeping both sides of it in close alignment. Following four nights of phone calls, words were added to the effect that nothing would hinder trade between Northern Ireland and the rest of the UK, nor the UK’s constitutional integrity.

The breakthrough was just about enough to get May over the line. On 15 December, the EU27 formally granted passage to the second phase of Brexit negotiations. The Conservatives, in a rare display of unity, praised May’s steely determination. Dublin regarded the deal as “bulletproof” and a “cast-iron guarantee” of no hard border.

A closer look, however, reveals that Dublin’s and London’s interpretations of the deal on the border are significantly different. Ireland regards “alignment” as a strict, legal concept, which binds Northern Ireland (and indeed the rest of the UK) to the EU’s regulatory sphere. The UK regards it as voluntary, flexible and minimalist.

A sober assessment was delivered by a senior EU official as the summit in Brussels drew to a close. “This is, and will remain, one of the very difficult issues… both because of the issue itself, on its own merits, but also because it exposes the contradictions in the UK position. That is, that you can’t at the same time have frictionless trade and be outside the customs union and the single market. The way to have frictionless trade is to be in those constructions. That’s why they were created.”

It will be difficult for many reasons. There is distrust between the DUP and Dublin. Unionists have lined up to accuse the Irish government of using Brexit to execute a land-grab, by seeking to drive a wedge between the north and Great Britain.

An opinion poll in early December reminded Fine Gael that a tough stance on a soft border is a vote winner. The DUP believes its hard-line stance on the alignment issue has played well with its base.

It is difficult to see this issue settling down. Ireland maintains an implied veto in the second phase of the negotiations, since progress will always require the consensus of the EU27. The EU believes that the three-way lock on Britain’s “no hard border” guarantee will constrain the free trade fantasies of Brexiteers.

On 1 December, the president of the European Council, Donald Tusk, met Leo Varadkar in Dublin. Afterwards, he said, “Let me say very clearly: if the UK offer is unacceptable for Ireland, it will also be unacceptable for the EU. I realise that for some British politicians, this may be hard to understand.” He added, somewhat enigmatically: “This is why the key to the UK’s future lies – in some ways – in Dublin, at least as long as Brexit negotiations continue.” l

Tony Connelly is RTÉ’s Europe editor and the author of “Brexit and Ireland” (Penguin Ireland, £14.99)