Labour MPs warned the Nationalists that they would be responsible for a hard Brexit if they did not back staying in a customs union, or a deal which would include single market membership. However, SNP MPs have already ruled out backing Conservative MP Ken Clarke’s motion on a customs union and party sources would not confirm whether they would support the Common Market 2.0 motion by Tory MP Nick Boles, which calls for an enhanced Norway-style deal of single market membership.

Joanna Cherry MP yesterday said the SNP were “looking very carefully at the detail” of the Boles motion but stressed they were just “proposals, not an agreement to be picked off the shelf”.

An SNP source later confirmed that Mr Clarke’s motion on a customs union would not be supported as it “fell far short of what was needed” and added that while the Boles “form of words have been strengthened” and were “closer” to a compromise position, they were “still discussing” whether to back it, as the “emphasis is on keeping Remain on the table”.

SNP MP Joanna Cherry, during the Brexit debate in the House of Commons, London.

Speaker John Bercow will this morning decide which of nine motions will be debated in the next series of indicative votes as the House of Commons seeks to find a way out of the Brexit stalemate.

The UK was due to leave the EU last week, but the Prime Minister’s Withdrawal Agreement has now been defeated three times and last week’s indicative votes did not produce a clear consensus in Parliament for a way forward. Mr Clarke’s motion on ensuring “a commitment to a permanent and comprehensive UK-wide customs union, which would be enshrined in law” – which lost by just six votes last week – will be presented again. The Boles motion has been “tweaked” to try to bring it closer to previous SNP demands for remaining in the single market to retain freedom of movement and will also be lodged again.

However last night Scottish Labour MP Ian Murray said the SNP needed to support the Clarke motion – and if they had done so last week it would have “given the PM a clear instruction on the way ahead”.

He said: “They must support it this week alongside a revocation backstop and a public vote. Similarly, the Boles motion is single market and customs union which is what they’ve always wanted.”

Mr Murray added that if the SNP did not back either “they will be responsible for failing to prevent a hard Brexit with a soft one which has always been their policy”.

He said: “If we can’t get what we want we must find a compromise for the benefit of the country and the SNP must stop playing games and see through their own policy.”

His Labour colleague Paul Sweeney MP said that it was now “critical” for all parties to “come together to stop a hard Brexit which remains the legal default”.

He added: “The first round of indicative votes suggests that a potential majority lies around a customs union and the Common Market 2.0 version. There will have to be compromises on all sides to build a majority for a way ahead and the SNP shouldn’t make the perfect the enemy of the good.”

He said Scottish Labour MPs had backed Ms Cherry’s motion of an emergency option to revoke Article 50 as a “safeguard” against a no-deal exit, but that the SNP now had to take “a similarly rational approach to reducing the risk of no deal by supporting a compromise option”.

But SNP Westminster leader Ian Blackford said MPs must use today’s indicative votes to keep remaining in the EU firmly on the table.

He said: “The UK Parliament must stop ignoring the people of Scotland and prevent a Brexit catastrophe – by voting to revoke Article 50, and call a halt to the Brexit process, or hold a second EU referendum with Remain on the ballot paper.

“There is now a very real prospect of preventing Brexit, and the decades of damage it would cause. Given everything we now know – staying in the EU must be the priority.”

Ms Cherry also revealed that Labour MPs had been working with her to find a more “palatable” way of wording her own proposal. Under the reworked motion, if the UK gets to 10 April, the date of a European Council summit, without a deal, an extension to Article 50 will be sought. If that extension is not granted, the UK government would then be mandated to put a vote on no-deal before the House of Commons.

Ms Cherry said: “We’re confident that that will be defeated, and the motion goes on to say that if the vote for no deal is defeated, the government must revoke Article 50.”

The reworked version also provides for a public inquiry to be set up within three months of revocation to look at Britain’s future relationship with the EU and whether a majority can get behind it. She added: “I’ve worked very closely with some Labour MPs who didn’t feel able to support the way it was worded last time to craft it into a form that’s more palatable for them. I have been proactively approached by many Labour MPs who didn’t vote for it last time who want to support it this time round.”

Pressure is also on Prime Minister Theresa May to accept a soft Brexit if Parliament unites around those motions. Justice Secretary David Gauke said she would have to “look closely” at any option that could command a majority. However Downing Street has said that the Prime Minister intends to bring her deal back to the House of Commons for a fourth vote.

SNP ‘could force hard Brexit’ if they fail to compromise on customs union