Theresa May is battling to overcome the obstacle of the so-called Brexit backstop plan for Northern Ireland as she prepares for another Commons vote on her withdrawal deal.
The Democratic Unionist Party (DUP), which props up the Conservative government in Parliament, has so far refused to support any Brexit deal that contains the backstop in its current form.
So what exactly is the row about and is there any way out of the impasse?
What is the Brexit backstop?
The backstop is a back-up plan, or position of last resort, to be implemented if a permanent trading arrangement is not agreed with the European Union during the 21-month transition period after the UK quits the EU. The aim is to maintain an open border on the island of Ireland, with few restrictions for goods and services crossing between Ireland and Northern Ireland.
Under the deal agreed between May and Brussels, the backstop would keep the whole of the UK very closely aligned to EU customs rules, with some regulatory differences between Northern Ireland and the rest of the UK.
The backstop is intended to be temporary but would remain in place “unless and until” alternative arrangements are agreed between the EU and UK that could then replace it, in whole or in part.
Following the rejection of May’s Brexit deal by Parliament, the UK government and the EU agreed an additional “instrument” on the backstop, “intended to address concerns that the UK could be made to remain in the backstop against its will”, says fact-checking site Full Fact.
However, the Government’s own legal advice says the UK might still be unable to exit the backstop if the future relationship negotiations fail. In practice, this means Britain could not unilaterally leave the backstop in the event of an impasse with the EU that was the result not of any demonstrable failure by either party but simply “intractable differences”.
Under the backstop, Northern Ireland would also be subject to much more stringent EU regulations than the rest of the UK – an arrangement that has greatly angered the DUP.
Why is the Brexit backstop necessary?
The goal of the backstop is “to protect the 1998 Good Friday Agreement to end the Northern Irish ‘troubles’ while ensuring the integrity of EU law”, says the Financial Times.
At present, goods and services are traded on the island between the UK and the Republic of Ireland with few restrictions. As both countries are currently part of the EU single market and customs union, products do not need to be inspected for customs and standards.
But after Brexit, “all that could change – the two parts of Ireland could be in different customs and regulatory regimes, which could mean products being checked at the border”, says the BBC.
Both the EU and the UK have said they do not want the return of border checks, but “the UK’s current red lines, which include leaving the customs union and the single market, make that very difficult” to avoid, adds the broadcaster.
So what happens next?
“We still have a huge difficulty with the backstop because we see it as a waiting room for constitutional change. We could find ourselves locked in there forever,” Jim Wells, a DUP member of the Northern Ireland assembly, told BBC Radio 4’s Today programme.
Despite the impasse, there are hopes of progress on the issue in the near future, with former Northern Ireland first minister David Trimble saying “substantive changes” have been made to limit the impact of the backstop.
In a new joint paper for the Policy Exchange think tank, Lord Trimble and the historian Paul Bew say that the Government is looking at technological alternatives to the measure and that new protections on the backstop, agreed by May and European Commission President Jean-Claude Juncker last week, have greater force than appreciated.
The paper shows that “the risk of the EU keeping the UK in the backstop to force it to agree to things it doesn’t want… is clearly now negligible”, says The Spectator’s James Forsyth.
And while “not a word” of May’s withdrawal agreement had been changed, agreement in the Commons was getting closer, Trimble and Bew write in their report. “A widespread war-weariness on all sides is a significant factor,” they add.
Is there an alternative to the current backstop?
The EU has said it would be willing to drop the UK-wide customs union at any point in exchange for a Northern Ireland-only backstop. But the prime minister has rejected this measure, because it would create an effective customs border in the Irish Sea and potentially regulatory disparity between Northern Ireland and the rest of the UK.
The EU and the UK, prompted by hardline Brexiteers, have committed to find alternative technological arrangements to avoid a hard border, but “both sides admit such solutions do not yet exist”, says the FT.