Democratic Unionist deputy leader Nigel Dodds has told the prime minister it is not too late to bin her Brexit deal.
Mr Dodds used his speech at the DUP’s annual conference to urge Theresa May to change course, warning that the proposed Withdrawal Agreement would see the UK assume a “pitiful and pathetic place”.
The party’s Westminster leader insisted the union of Great Britain and Northern Ireland was “non-negotiable”.
“It is still not too late for the Prime Minister to change course,” said the North Belfast MP.
“Don’t believe the propaganda that it’s too late - it isn’t.”
Mr Dodds, who spoke ahead of scheduled addresses by party leader Arlene Foster and former foreign secretary Boris Johnson, offered a scathing critique of the Irish border “backstop” proposal that would see Northern Ireland operate under a number of different regulatory rules to Great Britain if a wider UK/EU trade deal fails to materialise.
“The DUP wants a deal with the European Union, we understand that businesses, families and communities want certainty,” he told delegates.
“But it is not this deal. It is not a deal at any price. The prime minister used to say that. We still say that.
“So Prime Minister, the message from this conference, from every section of this party is - bin the backstop.”
He added: “In the coming weeks Parliament will be faced with a clear choice on the future of our country.
“To be a free independent trading nation leaving the EU as one United Kingdom or to be locked into an EU straitjacket, divided and diminished.
“The published Withdrawal Agreement portrays a pitiful and pathetic place for the United Kingdom.
“Hundreds of pages are devoted to a backstop which will bind the United Kingdom into taking the rules of the EU with no right to leave and no end date.”
Ms Foster will later tell delegates the draft EU Withdrawal Agreement contains arrangements that are not in Northern Ireland’s long-term interests.
The country would inevitably begin to diverge from its largest market, the rest of the UK, if it remained part of the EU’s customs code under the backstop arrangement, the DUP leader is expected to tell the party faithful.
Ms Foster has acknowledged the frustration of many in Northern Ireland’s business community with the pace of negotiations.
Her party has prided itself on its relationship with firms, but relations have been strained by their support for the draft UK-EU deal.
Ms Foster has warned that the DUP may revisit its confidence and supply deal to support the Conservatives in key votes at Westminster if the draft Brexit deal is voted through Parliament.
The position of Gibraltar had been one of the issues facing EU states attempting to agree a common position on UK withdrawal.
Spain is pressing for a guarantee over its say on the future of Gibraltar.
On Saturday morning, a government minister from Gibraltar told the DUP conference that the British territory “will not fold” in the face of Spain’s Brexit demands.
Samantha Sacramento was given a rousing reception by the DUP members as she insisted that Gibraltar will not be “bullied” by any bid from Madrid to undermine its sovereignty.
Housing and equality minister Ms Sacramento was standing in for Gibraltar’s chief minister, Fabian Picardo.
Mr Picardo had been due to address the party conference but the renewed focus on the British territory in the Brexit talks forced him to pull out to concentrate on the negotiations.