British Prime Minister Theresa May raised questions over whether the Irish backstop would be used by the European Union in a January 14 letter to EU leaders.
The backstop is a legally-binding device that ensures no hard border will emerge between Northern Ireland and the Republic of Ireland even in the event that no formal deal can be reached on trade and security arrangements.
May said in the letter that to avoid bringing the insurance policy into force, the UK would choose the application of a provisional trade agreement rather than defaulting to the backstop.
The government had said it would consider giving parliament the chance to vote against entering the backstop if it was ever triggered.
A letter from the EU aimed at providing reassurances to the British government over Brexit was published Monday.
Senior sources in Brussels told Euronews that the letter, written by European Council President Donald Tusk, outlined the EU’s aims regarding the Irish backstop — the most contentious part of the Brexit deal.
However, the sources say they are not optimistic that the letter will be enough to close the deal in the House of Commons tomorrow.
“The letter will offer clarifications and reassurances but not reopen or contradict the Withdrawal Agreement,” a source told Euronews.
“To be honest, I don’t see it converting the DUP or other hardliners," the source added.
This stance was proved right late on Monday morning when the DUP did indeed assert that the letter had come up short.
"The letter isn't legally binding," DUP deputy leader Nigel Dodds told BBC radio. "The prime minister will struggle to justify what the delay was about."
Three senior sources also confirmed that the letter, which will aim to convince MPs that they won’t be “trapped” in an EU Customs Union forever, won’t be legally binding.
However, it is “obviously intended to be a sincere and political commitment.”
The source believed that the real question regarding tomorrow's vote was whether there was "a big or small margin of defeat, as I think that's what will influence or decide what PM does next.”