Theresa May is today facing a “humiliating defeat” on her compromise Brexit Plan as she warned MPs that the biggest threat to the Union was now a no-deal outcome.

As Westminster prepares for its most momentous day for generations, loyal Conservative MPs said the Government’s game-plan was to “manage the margin of defeat and keep it as low as possible,” so that a tweaked version of the Prime Minister’s proposal might have a chance of succeeding at a second attempt.

Last night at a private party meeting, Mrs May told Tory MPs they needed to deliver on Brexit while preventing a Labour government. One minister explained: “She said we have got to keep Jeremy Corbyn as far away as possible from No 10; to do that, we have got to come together."

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This morning, John Bercow, the Commons Speaker, will decide which of a string of amendments will be voted upon, including one to guarantee a no-deal outcome is avoided and one to ensure the Irish backstop ends by December 31 2022.

If such amendments were passed, the margin of the defeat on Mrs May’s plan could be reduced significantly.

The Daily Telegraph quoted one Cabinet source as saying it would be "hard for her to carry on" if she lost by more than 100 votes.

The Leader of the House Andrea Leadsom insisted Mrs May was determined to continue fighting for her agreement in the best interests of the country.

"Anything that looks like that level of disruption would incredibly bad - both for the country and for Brexit," she told BBC2's Newsnight.

"So I think the Prime Minister will remain determined to deliver on this deal. Her purpose is to leave the European Union in line with what people voted for. She could not be clearer about that."

The deal suffered its first official parliamentary defeat in the House of Lords on Monday night as peers voted by 321 votes to 152 - a majority of 169 - to reject it.
Mr Corbyn indicated he was finally ready to table a vote of no-confidence in the Government if it loses in the Commons.

In Scotland, Nicola Sturgeon tried to bolster the Conservative rebels and opposition Remainers by insisting: “The chances of remaining are at their highest since the EU referendum.”

The First Minister declared: “MPs must come together to vote down this bad deal, rule out no-deal, extend the Article 50 process and call another referendum. This opportunity must be grasped.”

In a speech in Leave-supporting Stoke-on-Trent, Mrs May urged Conservative colleagues to back her plan “for the country's sake," warning them a refusal to do so would be the "height of recklessness".

However, Government whip Gareth Johnson defied his leader by quitting, saying it was clear there had been "no significant change" to the Withdrawal Agreement.

This followed the publication of the EU’s letters, which, the PM claimed offered "valuable new clarifications and assurances,” which would help assure MPs their fears were misplaced. The letters carried "legal force," she insisted, and made “absolutely clear the backstop is not a threat or a trap".

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But Labour’s Keir Starmer dismissed the letters as a mere “reiteration of the EU's existing position” while Nigel Dodds for the Democratic Unionists said they were “meaningless”.

Later in a Commons statement, Mrs May urged colleagues to “take a second look” at her plan.

“It is not perfect but when the history books are written, people will look at the decision of this House tomorrow and ask: 'Did we deliver on the country's vote to leave the EU, did we safeguard our economy, security or Union, or did we let the British people down?’"

The PM also warned a no-deal Brexit would “strengthen the hand of those campaigning for Scottish independence or indeed those demanding a border poll in Northern Ireland,” noting: “Surely, this is the real threat to our Union.”

Jeremy Corbyn claimed Mrs May had "completely and utterly failed" to allay MPs' concerns about her Brexit Plan.

He said the Brussels letters did “not give the legal assurances this House was promised and contain nothing but warm words and aspirations".

The Labour leader complained: “She has not once tried to work with Parliament to construct a Brexit deal that this House and the country can support and now she is left facing a humiliating defeat and is blaming everybody but herself.”

He added: “The Government is in disarray; it's clear if the Prime Minister's deal is rejected tomorrow, it's time for a general election; it's time for a new government."

Ian Blackford for the SNP insisted the offer from Brussels on further assurances was a humiliation for Mrs May.

“The Prime Minister is simply in fantasy land, presenting her statement as bringing changes when it does not. This Government must stop threatening no-deal. It is time to face reality; extend Article 50 and let the people decide.”

Mrs May hit back, arguing the interests of Scotland were best served by ensuring Scotland remained part of the UK.

“If the Scottish National Party is so clear that politicians should listen to the voice of the people, it should listen to the voice of the Scottish people expressed in the referendum in 2014 and abandon the idea of independence,” she declared.

In other developments:

*Dominic Raab, the former Brexit Secretary, urged MPs to vote against the PM’s plan as he criticised "scaremongering" around a no-deal exit;

*Boris Johnson, the former Foreign Secretary, said any move by Parliament to try and frustrate Brexit would be seen by voters as a "betrayal" by the "deep state";

*a cross-party group of anti-Brexit politicians published proposed legislation to bring about a second referendum;

*Esther McVey, the former Work and Pensions Secretary, said if Mrs May lost today’s vote, she should go back to Brussels and demand a better deal for the £39 billion divorce bill and

*Ireland’s Leo Varadkar said he remained hopeful a deal could be agreed, noting: “It's important we allow the British political system the time to make that decision.”