BORIS Johnson is urging MPs to back his “great new deal” to remove Britain from the EU on October 31 as the political battle now switches from Brussels to Westminster.

But Northern Ireland’s Democratic Unionists made clear they could not vote for the deal in the proposed Saturday sitting of the Commons, saying it undermined the Union of the United Kingdom and “drives a coach and horses through the professed sanctity of the Belfast Agreement” because it removes the need for consent by both Unionists and Nationalists in favour of majority rule.

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They said the proposals were “not beneficial to the economic well-being of Northern Ireland and they undermine the integrity of the Union”. Their concerns rest mainly on the removal of a veto the DUP has and what they see as a customs and regulatory border down the Irish Sea, setting Northern Ireland apart from the rest of the UK.

The Prime Minister announced the new Withdrawal Agreement and Political Declaration on the way forward beyond Brexit despite the DUP’s firm opposition.

No 10 made clear there would be a Commons vote today to hold a Saturday sitting of the UK Parliament for MPs to vote for the new deal. But, at present, it is hard to see where the Prime Minister gets the parliamentary numbers from to get so-called “Meaningful Vote 4” through the House.

Discounting Sinn Fein, which does not take its seats, the Speaker and his deputies, who do not vote, as well as the tellers, who also do not vote, then the magic number is 318 to get a majority.

The Tories have 285 votes. Even with the DUP, this leaves Mr Johnson 23 short. Some former Tory MPs now sitting as independents could rally round the new deal – there are 21 of them – but it seems clear the PM might have to rely on a handful of Labour rebels to get Brexit over the line.

Yet without the DUP, the task of succeeding where Theresa May failed on three occasions seems extremely difficult if not impossible.

The PM’s spokeswoman said: “His view is this deal is the best way through for the whole of the UK and he hopes MPs will support it on Saturday.”

Asked how Mr Johnson was going to get his deal through the Commons given the parliamentary arithmetic, she said: “We want all MPs to support us. The PM believes this is the best way forward for the whole of the UK, it protects the Union, it removes the backstop and deals with the unique circumstances on the island of Ireland. MPs this weekend have an opportunity to back a deal that means the UK leaves the EU in an orderly way.”

Asked if Mr Johnson was confident of winning the vote, the spokeswoman referred to her earlier answer.

She said the PM had been in “regular contact” with the DUP and spoke this morning twice to Jean-Claude Juncker, the European Commission President, as well as Cabinet colleagues on the EU Exit Strategy Committee whose membership numbers just five, including the Chancellor, Brexit Secretary and Attorney General.

Mr Johnson, is due to arrive in Brussels this afternoon, said: "We've got a great new deal that takes back control, now Parliament should get Brexit done on Saturday so we can move on to other priorities like the cost of living, the NHS, violent crime and our environment."

He added: "We will leave the EU's customs union as one United Kingdom and be able to strike trade deals all around the world. This is a deal which allows us to get Brexit done and leave the EU in two weeks' time."

Mr Johnson declared the "anti-democratic" backstop had been abolished.

"The people of Northern Ireland will be in charge of the laws that they live by, and, unlike the backstop, will have the right to end the special arrangement if they so choose," he added.

Mr Juncker tweeted: "Where there is a will, there is a #deal - we have one! It's a fair and balanced agreement for the EU and the UK and it is testament to our commitment to find solutions. I recommend that #EUCO endorses this deal."

Jeremy Corbyn was quick to dismiss the deal.

Speaking during a visit to Brussels, the Labour leader said: "This is a day where the Prime Minister seems to have made a deal with the European Union which doesn't give us the complete freedom of movement between Britain and Ireland because it creates a customs union border down the Irish Sea.

"As it stands we cannot support this deal. Also it is unclear whether it has the support of his allies in the DUP, or indeed many of his allies on his own backbenches.

"From what we know, it seems the Prime Minister has negotiated an even worse deal than Theresa May's, which was overwhelmingly rejected," he added.

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Nicola Sturgeon confirmed SNP MPs would not back the PM’s new Brexit deal as she insisted it would mean Scotland alone was "treated unfairly" when the UK left the EU.

The First Minister said it was "democratically unacceptable" for Scotland to be facing an outcome it did not vote for and it was now "clearer than ever" the best future for Scotland was as an independent, European nation.

Jackson Carlaw, the Scottish Conservatives’ acting leader, urged the SNP to get behind the deal, insisting it was "time to get Brexit sorted".

He tweeted: "If Labour and SNP MPs are against us leaving without a deal, then it's time to back this one. The country needs to move on. #GetBrexitDone."