Theresa May would never agree a Brexit deal with the EU which “traps” the UK permanently in a customs union, Downing Street has said.
The pledge came amid speculation over possible ministerial resignations if the Prime Minister gives too much ground ahead of a crunch Brussels summit next week.
European Commissioner Guenther Oettinger said on Friday that “it does appear possible there will be a breakthrough” at the October 17-18 summit, fuelling speculation that a deal is near on a so-called “backstop” for the Irish border.
It is understood that a number of ministers voiced concern at a meeting with the PM in Downing Street on Thursday that any such backstop could leave the UK in an open-ended customs union, preventing it from seeking trade deals elsewhere in the world.
Former foreign secretary Boris Johnson has said it risks making the UK a “permanent EU colony”.
Meanwhile, Chancellor Philip Hammond became the first senior Government figure to suggest that the backstop - designed to keep the border between Northern Ireland and the Republic open in the case that no broader EU/UK trade deal is finalised - will “probably” have to come into effect for a period.
But the Democratic Unionist Party, which props up Mrs May’s minority Conservative administration in the House of Commons, urged her to resist any initiatives from Brussels which might threaten the Union.
DUP Brexit spokesman Sammy Wilson said there would be “consequences” for Mrs May if she walked away from her promise to protect the Union.
“We are simply reminding her, you are being torn at the moment between what we believe are your gut instincts and your sound principles on the Union and at the same time the bullying, threatening behaviour of the EU,” said Mr Wilson at a meeting of DUP MPs and Assembly members in Portadown.
“Go with your principles, go with your instinct, go with your responsibility to the people of the UK and show the EU negotiators the door.”
Mrs May chaired a meeting of the inner Cabinet on Brexit progress Mrs May set out in June proposals for a “temporary customs arrangement” to ensure that the border between Northern Ireland and the Republic remains open in the case that no broader EU/UK trade agreement has been finalised.
The document stated that the UK Government “expects” this arrangement to remain in place no later than the end of December 2021.
But the EU is mounting resistance to any specific time limit being included in the text of the UK’s Withdrawal Agreement, while Leave-backing ministers are understood to be insistent that the end of the arrangement should be more precisely defined than the vague term “temporary”.
As officials continued to wrangle over the precise wording of the agreement in Brussels, a Downing Street spokeswoman told a Westminster media briefing: “The Prime Minister would never agree to a deal which would trap the UK in a backstop permanently.”
The spokeswoman said Mrs May stood by her June proposals, adding: “Our position is that this future economic relationship needs to be in place by the end of December 2021 at the latest.”
Leading Conservative Brexiteer Steve Baker responded that any backstop which went beyond a simple free trade agreement amounted to “effectively committing the UK to membership of the single market and customs union”.
Mr Baker said: “That won’t wash. The British people voted to take back control over money, laws borders and trade.”
Downing Street has always been clear that it does not wish or expect the backstop option to be implemented, as it insists it will be possible to agree a wider trade deal guaranteeing an open border in Ireland by the end of the transition period in December 2020.
But Mr Hammond told Bloomberg TV: “We are not going to remain in anything indefinitely, we are very clear this has to be a temporary period.
“But it is true that there needs to be a period, probably following the transition period that we have negotiated, before we enter into our long-term partnership, just because of the time it will take to implement the systems required.
“It’s very important to us that business doesn’t have to make two sets of changes, that there will be effectively continuity from the current set-up through the transition period into any temporary period and then a single set of changes when we move into our long-term new economic partnership with the European Union.”
Following Thursday’s meeting of the “inner Cabinet” in Downing Street on Thursday, Government Chief Whip Julian Smith insisted ministers were united behind the PM’s strategy.
However, Westminster was rife with speculation of possible resignations by hardline Brexiteers within the Government.
Earlier, Work and Pensions Secretary Esther McVey, who was not at the Downing Street meeting, pointedly refused to endorse the Prime Minister’s Chequers blueprint for Brexit.
International Development Secretary Penny Mordaunt and the Leader of the Commons Andrea Leadsom - who, like Ms McVey, both backed Leave in the referendum in 2016 - were also said to harbour deep concerns.
A number of ministers, including Foreign Secretary Jeremy Hunt, Brexit Secretary Dominic Raab, Environment Secretary Michael Gove and International Trade Secretary Liam Fox, were said to have raised concerns over the backstop issue during the 90-minute meeting.