RUTH Davidson has today piled the pressure on Theresa May over Brexit by making clear any “regulatory alignment” with the EU on trade should not just apply to Northern Ireland but to the whole of the UK.

The significant intervention by the leader of the Scottish Tories comes just hours after Scottish Conservative MPs made clear to the Prime Minister that there had to be changes to her flagship EU Withdrawal Bill to protect devolution and the Union.

As Mrs May prepared to speak to Arlene Foster, the leader of the Democratic Unionist Party, to try to get the Brexit process back on track, Ms Davidson issued a statement about the key issue of trade regulation post Brexit.

The Scottish Tory leader, who backed Remain in the 2016 EU referendum, said: “The question on the Brexit ballot paper asked voters whether the UK should stay or leave the European Union; it did not ask if the country should be divided by different deals for different home nations.

“While I recognise the complexity of the current negotiations, no government of the Conservative and Unionist Party should countenance any deal that compromises the political, economic or constitutional integrity of the United Kingdom.”

The Edinburgh MSP pointed out how all sides had agreed that there should be no return to the borders of the past between Northern Ireland and the Republic of Ireland but she stressed that, similarly, jeopardising the UK's own internal market was in no-one's interest.

Ms Davidson then added: “If regulatory alignment in a number of specific areas is the requirement for a frictionless border, then the Prime Minister should conclude this must be on a UK-wide basis.”

Mrs May is now engaged in a race against the clock to find the key to break the deadlock in the Brexit talks.

Her hopes of securing agreement on the terms of Britain's EU withdrawal were dashed on Monday when the DUP refused to accept proposals which would have shifted Northern Ireland's customs border to the Irish Sea.

Mrs May is planning to return to Brussels before the end of the week, with time running out to persuade leaders of the remaining 27 EU nations at a summit on December 14/15 that "sufficient progress" has been made on divorce issues to move Brexit negotiations on to their second phase. This will deal with trade and the transition to a new relationship.

Today she is expected to speak by phone with Ms Foster as she grapples to find a form of words acceptable to the Northern Irish party, on which she relies to prop up her minority administration at Westminster.

Mrs May had to break off from talks with European Commission president Jean-Claude Juncker on Monday for an urgent call with the DUP leader, after she dramatically declared her party's implacable opposition to proposals which would have imposed "regulatory alignment" between Northern Ireland and the Republic in order 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 Mrs Foster's eleventh-hour intervention. He said he was "surprised and disappointed" by Mrs May's request for more time.

European Council president Donald Tusk confirmed that, until the surprise developments at Stormont, he had been preparing to issue new negotiating guidelines for the second phase of talks on Tuesday.

It is also understood that differences also remain between the EU and Britain over the issue of European Court of Justice jurisdiction over EU nationals living in the UK after Brexit.

Mrs May insisted she was still "confident" of getting a green light for trade talks at next week's summit.

Failure to do so would risk throwing the whole Brexit process into crisis, as many companies are 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.

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 - and in some cases parliaments - before convening in Brussels.

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."

First Minister Nicola Sturgeon has made clear that if a special deal on single market access can be done for Northern Ireland, then one should be done for S Outland too.

Labour leader Jeremy Corbyn said the failure of talks showed Mrs May's Government was "completely ill-equipped to negotiate a successful Brexit deal for our country", while former Ukip leader Nigel Farage said she should "leave office now".

But many Conservatives were optimistic of a deal being struck.

The chairman of the Commons Northern Ireland Committee, Tory MP Andrew Murrison, told BBC2's Newsnight: "We understand that later this week there is every prospect of a deal satisfying the European Union that, in its words, sufficient progress has been made which will set us up for a favourable conclusion to the summit.

"The mood here at Westminster at the moment is far more upbeat than I've known it for some considerable time now. I think, with compromise on both sides ... we are set fair for some good news before Christmas."

Irish agriculture minister Michael Creed told Newsnight that "with goodwill on all sides" a deal could be agreed by Friday, but added: "I don't want to underestimate the significance of the issues that have yet to be agreed."

But ormer top Foreign Office official Lord Ricketts said the row was "damaging" for Mrs May and will leave EU leaders with the impression that she lacks the authority to get through Brexit negotiations.

He 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 in Brussels that the Prime Minister hasn't got authority over her own side and that will knock confidence in doing a final deal."

The crossbench peer added: "It leaves an impression that the Prime Minister hasn't got the authority to get through these difficult negotiations."

Former Brexit minister David Jones said: "There will be people in Downing Street who will have regretted not making the position clearer with the DUP."

He urged ministers not to "ignore the parliamentary arithmetic" in which the DUP props up the minority Government, while making clear he also opposed regulatory alignment as it would hinder Britain's ability to strike new free trade deals around the world.

"We need to ensure that the DUP are on board with whatever is proposed and I think it's fairly clear that yesterday they were not on board - the fact that they managed to stall the negotiations yesterday, I think, demonstrates the precise strength of their position so I don't think it should be under-estimated at all," he added.