DUP leader Arlene Foster has accused the EU and Ireland of “intransigence” that could lead to a no-deal Brexit.
Theresa May will use a speech in Northern Ireland on Tuesday to insist she can secure a Commons majority for a Brexit deal that “commands broad support” as efforts continue to find an alternative to the backstop.
May will acknowledge that it is a “concerning time” but “we will find a way to deliver Brexit” that honours commitments including avoiding a hard border with Ireland.
On Wednesday May will hold talks with Northern Ireland’s political leaders, including Foster.
The DUP leader said this morning the backstop as currently proposed was “toxic”.
“We will be reiterating our opposition to the current backstop. And the fact that parliament has now backed that position means that she has a clear mandate to go back to Brussels,” Foster told BBC Radio 4′s Today programme.
“Parliament’s mandate is to replace the backstop,” she said. “It would cause the break-up of the United Kingdom into the medium and longer term.”
Asked whether her stance on the backstop could force a no-deal Brexit, Foster said: “Well actually, I could reverse that by saying through the intransigence of the European Union and the Republic of Ireland in their attitude, they are actually more likely to bring about the very thing that they want to avoid.”
May is due to travel to Brussels on Thursday to meet European Commission president Jean-Claude Juncker.
Meanwhile in Westminster, the working group bringing together senior Eurosceptic and former Remain-supporting Tories will continue efforts to agree alternatives to the backstop.
Talks involving Conservatives including Brexiteers Iain Duncan Smith, Theresa Villiers, Steve Baker and Owen Paterson along with former Remainers Nicky Morgan and Damian Green will continue in Whitehall, chaired by Brexit Secretary Stephen Barclay.
The first meeting on Monday was described as “detailed and constructive” by the Brexit department.
But Brussels has restated its opposition to any attempt to reopen the Withdrawal Agreement, insisting the backstop was the “only operational solution” to the border question.
In her speech, May will say: “I know this is a concerning time for many people here in Northern Ireland.
“But we will find a way to deliver Brexit that honours our commitments to Northern Ireland.”
The backstop is effectively an insurance arrangement required by the EU to ensure the border between Northern Ireland and the Republic remains open if no wider deal is agreed on future UK/EU trade.
It would see the UK enter into a temporary customs union with the EU if no trade deal is sealed by the end of a transition period after Brexit, which lasts until December 2020 and could be extended to the end of 2022.
Northern Ireland would also abide by EU single market rules on goods, to avoid any need for regulatory checks of products crossing the border.
But critics fear the arrangements could lead to the UK being trapped indefinitely in a customs union, scuppering future trade deals with markets around the world.
And the DUP strongly rejects any measure which could lead to divergence between Northern Ireland and the rest of the UK, effectively creating a regulatory border in the Irish Sea.
MPs voted last week to say they would only back May’s Withdrawal Agreement if the backstop was replaced by “alternative arrangements”.