Ireland's Prime Minister Leo Varadkar (pictured) on Monday said he was "disappointed" after the UK pulled out of an agreement on the status of the Irish border at the last minute.

"I am surprised and disappointed that the British government now appears not to be in a position to conclude what was agreed earlier today," Varadkar told reporters in Dublin.

Earlier Monday, the UK appeared to agree for Northern Ireland to continue applying European single market and customs union rules to avoid a hard border with the Republic of Ireland post-Brexit.

'Regulatory divergence'

The draft text on Ireland reportedly stated that the "UK will ensure continued regulatory alignment to the rules of the internal market and customs union which, now or in the future, support North-South cooperation and the protection of the Good Friday agreement."

Although the precise definition of "regulatory alignment" remains unclear, it was believed to refer to the select single market rules that support ongoing co-operation between Northern Ireland and the Republic.

Read more: Northern Ireland's fragile peace 'all about the border'

However, Arlene Foster, who heads the Democratic Unionist Party (DUP) in Northern Ireland that forms part of the British government, said they would not accept a different status than that of the entire UK, effectively torpedoing hopes of a deal.

"We will not accept any form of regulatory divergence which separates Northern Ireland economically or politically from the rest of the United Kingdom," said Foster.

Northern Ireland's changing border The Irish Free State Britain's response to Irish demands for independence was devolution within the UK, or home rule. Pro-British Unionists didn't want to be governed by Dublin, so two parliaments were set up, for Northern and Southern Ireland. However, nationalists still pushed for full independence and in 1922 Southern Ireland was superseded by the Irish Free State as enshrined in the Anglo-Irish Treaty (pictured).

Northern Ireland's changing border The Six Counties Northern Ireland had been carved in a way that allowed Protestant loyalists to stay in control, but also ensure the region was large enough to be viable. It included four majority-Protestant counties in the ancient province of Ulster, as well as the two Catholic nationalist counties. Three of Ulster's counties — Donegal, Monaghan and Cavan — were placed on the Southern Ireland side of the border.

Northern Ireland's changing border No laughing matter? Involving members of the British, Irish and devolved Belfast governments, a 1924-25 boundary commission looked at the whether the border should stay where it was. It broadly remained in the same place, often cutting through communities across its 310 miles. The Spike Milligan novel "Puckoon," made into a film (above), charted the problems brought to a fictional Irish village divided by the border.

Northern Ireland's changing border Roadside customs checks The new border's checkpoints initially regulated the movement of certain goods, with movement of people being free. However, the Anglo-Irish Trade War of the 1930s saw tariffs imposed on foods and later coal and steel. The dispute ended in 1936, but Ireland still pursued protectionist policies into the 1950s. Customs stayed in place until the advent of the EU Single Market in 1993.

Northern Ireland's changing border Bloody legacy With an escalation in fighting in Northern Ireland in 1969, British troops were sent to the province, fueling nationalist resentment. The border was heavily guarded to stop weapons smuggling from the Republic. The South Armagh stretch was particularly notorious. The Irish Republican Army's South Armagh Brigade is thought to have killed about 165 British troops and police from 1970 to 1997.

Northern Ireland's changing border South of the Border The border was also policed by the Republic of Ireland's security forces, who intensified their anti-terror efforts in the late 1970s. They worked with the British, but the working relationship was not an easy one. To communicate with Irish counterparts, British troops at one time had to speak to the Northern Irish police, who would contact the Irish police, who would then call the Irish army.

Northern Ireland's changing border Watchtowers and rifle sights Despite the end of customs in 1993, the threat of terror still loomed and the border remained militarized, with watchtowers and soldiers. After the 1998 Good Friday Agreement — which brought back devolved government to Northern Ireland and sought to address issues such as policing and paramilitarism — the IRA eventually halted its campaign of violence as border security disappeared.

Northern Ireland's changing border Barely noticeable The border today is as invisible as it has ever been, with free movement of traffic between the Republic and the North. The picture shows two policemen, one British, one Irish, watching as a foreign leg of the 2014 Giro d'Italia crosses the border in Armagh.

Northern Ireland's changing border Anything to declare? There are fears that Brexit would make a hard border necessary, given that Britain appears set to leave the EU Customs Union and Single Market. The border issue is one of three conditions laid out by the EU for trade talks to begin. Brussels says there must be no hard border. Campaigners, like those pictured above, have sought to remind the public of what such a frontier would look like. Author: Richard Connor



Open border only

The Irish government had sought such a commitment. Earlier on Monday, Ireland’s Europe minister, Helen McEntee, told the BBC that Ireland would reject any proposals that didn't guarantee that the border between Northern Ireland and the Republic remained open.

Read more:The Irish border — what you need to know

Britain is aiming to strike an agreement on the progress of Brexit negotiations so that talks can move on to the next-phase discussion over a post-Brexit trade deal.

Before the deal fell through, the British team reportedly insisted that the phrase "no regulatory divergence" be changed to "regulatory alignment," as the former would have insinuated that Northern Ireland would have to continue accepting all EU single market rules.

Three outstanding issues

The text on Ireland is part of a paper entitled "The Joint Report from the European Commission and the United Kingdom Negotiators on Progress."

Alongside the Irish border issue, Britain's financial settlement and EU citizens' rights are also under contention.

The EU negotiation team had given Britain until Monday to prove that sufficient progress had been made in the Brexit negotiations to advance talks.

Read more: Brexit poll: Half of Britons support second referendum

Elmar Brok, a member of the European parliament's Brexit group, said he believed there was a "very good chance" of a comprehensive Brexit deal. Brok added that he was "astonished" at how far the negotiations had progressed and that differences remained over "just a few words."

Brexit negotiations: What are the key issues? Two phases EU leaders agreed to negotiating guidelines during a summit in April 2017 that divided the divorce talks into two phases. Phase I, in which both sides aimed to settle the basic terms of Britain's departure, started in July and ended with an agreement on "sufficient progress" in December. Officials are now holding Phase II negotiations on the post-Brexit relationship between Britain and the EU.

Brexit negotiations: What are the key issues? The "Brexit Bill" London agreed to a formula for calculating what it owes in its "divorce bill" to the EU in early December after months of haggling by British officials. The current EU budget expires in 2022 and EU officials have said the divorce bill will cover financial obligations Britain had committed to before triggering article 50. The final bill will reportedly total around £50 billion (€67 billion).

Brexit negotiations: What are the key issues? Citizens' rights Both sides agreed in early December that the 3 million EU citizens currently in Britain and the 1.1 million British citizens in the EU keep their residency rights after Brexit. British courts will have immediate jurisdiction over EU citizens living in Britain. But the EU's highest court, the ECJ, can hear cases until 2027 if British judges refer unclear cases to them.

Brexit negotiations: What are the key issues? The Irish border Britain and the EU also agreed in December that no border checks between the Republic of Ireland and Northern Ireland would return post-Brexit. How feasible the commitment will be is unclear, as Britain's commitment to leaving the EU Single Market and Customs Union makes it difficult to avoid customs checks at the Irish border.

Brexit negotiations: What are the key issues? Transition period Theresa May envisages a two-year transition period after March 2019. Both sides still have to hash out the details of the transition period in Phase II, including the exact end-date, whether new EU laws passed during the period will apply to Britain, and whether Britain can negotiate its own free trade deals. British officials hope to agree on the terms of the transition by March 2018.

Brexit negotiations: What are the key issues? Trade May has repeatedly said Britain will leave the European Single Market and the EU Customs Union. Leaving both could disrupt British-EU trade, but allow Britain to negotiate its own free trade deals and restrict EU migration — key demands by pro-Brexit politicians. London has said it wants to negotiate a new EU-UK trade deal during Phase II to minimize trade disruption before March 2019.

Brexit negotiations: What are the key issues? Immigration Britain has also vowed to restrict EU migration into Britain after Brexit. However, some British lawmakers are wary that a sharp drop in immigration could lead to shortfalls in key sectors, including health, social care and construction. The EU has warned that Single Market access is out of the question if London decides to restrict the ability of its citizens to live and work in Britain.

Brexit negotiations: What are the key issues? Security Recent terror attacks across Europe including a string in Britain underline both sides' support for continued security cooperation after March 2019. But access to EU institutions such as Europol and programs such as the European Arrest Warrant require compliance with EU laws. Whether Britain will still be compliant after it leaves is unclear. Author: Alexander Pearson



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