DUP deputy leader Nigel Dodds has urged the prime minister to hold to her pledge that Northern Ireland will not be carved off from the rest of the UK economically post-Brexit.
Theresa May has insisted that a Brexit deal is still “achievable” despite deadlock in negotiations just days ahead of a crunch European Council summit.
Mrs May called for “cool, calm heads to prevail” after talks at the weekend failed to bridge differences between the UK and EU over the future status of the border on the island of Ireland.
The PM was addressing the Commons just two days before she travels to Brussels for a summit at which it had initially been hoped to finalise the UK’s withdrawal agreement as well as a political declaration on future trade and security relations.
Following the failure to achieve a breakthrough when Brexit Secretary Dominic Raab met EU chief negotiator Michel Barnier on Sunday, the European Commission confirmed that no further negotiations will be held ahead of Wednesday’s summit.
In a question to the PM after her statement to MPs on Monday, DUP Westminster leader Mr Dodds said it “could never be right” for a border to be placed in the Irish Sea.
The North Belfast MP quoted the Scottish Tory leader Ruth Davidson, who said she could not support any deal which creates a border between NI and GB.
And he asked for PM to confirm any deal which separated from the UK’s own internal market “could never be accepted by her”.
Mr Dodds added: “She has said that today. Will she confirm it is single market and customs union, the UK leaving the EU together with no part hived off either in the single market or customs differences?”
Mrs May vowed that the UK would leave the EU together, but said a deal which allowed Northern Ireland to export freely to both GB and the EU would be beneficial to business.
“I am very clear there should be no hard border between Northern Ireland and Ireland but as we put forward proposals we can deliver on that and maintain the integrity of our Union,” she said.
“And we have made that very clear when the EU made their proposal which would have effectively carved Northern Ireland away from the rest of the UK in their backstop proposal.
“It is precisely why we can not accept their backstop to the backstop because they continue to want to see that. In fact what we want to see in a backstop is a situation where Northern Ireland businesses can both export freely to Great Britain and the EU. Actually that would be a good position for the Northern Ireland businesses.”
Mr Dodds did not appear to be particularly convinced by her answer.
South Belfast DUP MP Emma Little Pengelly later asked Mrs May for a firm commitment that “nothing would be agreed with the EU that would exclude Northern Ireland from any future trade deals”.
The PM said any future trade deals would be on behalf of the whole UK, including Northern Ireland.
In a statement released on Monday evening, Mr Dodds said it was not just the DUP who did not support a border down the Irish Sea, again referring to Ms Davidson’s comments.
He added: “The prime minister must hold to her statement today and with her previous clear statements that there can be nothing which interferes with the constitutional and economic integrity of the United Kingdom.
“It is clear there are voices from all parts of the United Kingdom, from those on different sides of the referendum argument, and from different political parties who all realise that placing a border down the Irish Sea would gradually push the United Kingdom apart.”
Meanwhile, DUP MLA Christopher Stalford pointed out on Twitter that the PM had been asked four times about publishing a date when the proposed backstop would end, and described her refusal to answer the question as “slippery”.
It was also reported that eight MPs asked for a reassurance on a time-limit – something the EU has resisted, and none “got a clear answer”.
Ulster Unionist MEP Jim Nicholson said the PM “must deliver on her commitments to the Union” in negotiations, and insisted that “words alone are not enough especially at this late stage”.