Theresa May was scrambling to salvage her Brexit deal on Tuesday after her Northern Irish political partners pulled the plug on her attempt to secure a withdrawal agreement with the EU.

The Prime Minister was set to call the leader of the Democratic Unionist Party to convince her to back her proposals for what should happen with Northern Ireland’s land border after Brexit.

Downing Street indicated Ms May hoped to be back in Brussels before the end of the week to secure the agreement, after the DUP refused to accept plans that could have seen Belfast following a different regulatory regime than London.

The Prime Minister was set to brief her Cabinet on Tuesday amid fallout of from the delay, as an ex-senior Foreign Office official said the row had been “damaging” for Ms May.

She has insisted she is still “confident” of securing a withdrawal deal, allowing her to get a green light for trade talks at the European Council summit starting December 14.

Failure to do so would risk throwing the whole Brexit process into crisis, with companies believed to be preparing to activate contingency plans to start moving staff and activities out of the UK if there are no signs of progress by Christmas.

It would also call into question her leadership, with backbenchers setting progress in the talks as a key test Ms May must pass to stay in power.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

EU officials are understood to believe that a text of the deal must be thrashed out by the end of the week to allow it to be included in draft summit conclusions and give other leaders time to consult their own governments before convening in Brussels.

Former Foreign Office official Lord Ricketts said the row will leave EU leaders with the impression Ms May lacks the authority to get through Brexit negotiations.

The crossbench peer told BBC Radio 4's Today programme: “I mean, it's pretty extraordinary that this wasn't all stitched up with the DUP beforehand.

“We're used to prime ministers going to Brussels and having a row with the EU and coming back without an agreement, but to go agree with the EU and then have a row on your own side is inconvenient.”

He went on: “It leaves an impression, I think, in Brussels that the Prime Minister hasn't got authority over her own side and that will knock confidence in doing a final deal.”

Former Brexit minister David Jones said that the DUP’s intervention “demonstrates the precise strength of their position”.

Brexit: No deal in Brussels after Theresa May and Jean-Claude Juncker meeting to break deadlock

Ms May had to break off from talks with European Commission president Jean-Claude Juncker on Monday for an urgent call with the DUP leader Arelene Foster, who declared her party's opposition to proposals on the table.

The plans would have imposed “regulatory alignment” between Northern Ireland and the Republic to avoid the need for a hard border.

Irish premier Leo Varadkar said that the deal had been agreed by the European Commission, UK and the Republic before the process was thrown into disarray by Ms Foster's eleventh-hour intervention.

Irish Prime Minister, Leo Varadkar, during a press conference in Dublin (EPA)

Prominent Tory MPs voiced their opposition to any deal which threatened the territorial integrity of the United Kingdom by forcing Northern Ireland to operate under different regulations from the mainland.

Leading Brexiteer Jacob Rees-Mogg said: “I don't think that can possibly happen. The Government doesn't have a majority for that.”

Leaders of devolved administrations in Scotland, Wales and London said they would want the option to adopt in their parts of the UK any special status afforded to Northern Ireland.