Prime Minister Theresa May was facing a significant and potentially catastrophic defeat on a major Brexit vote in Parliament Tuesday, a defeat that could eventually lead to anything from no Brexit at all to a general election -- as May's allies took a page from “Game of Thrones” and ominously warned: “Winter is Coming.”

Parliament will vote later Tuesday on May’s withdrawal agreement with E.U. leaders, ahead of Britain’s scheduled departure from the bloc at the end of March. It is a vote that May is expected to lose heavily, but the severity of the loss is likely to determine the extent to which May is able to go back to Brussels and demand further concessions to try again to get the agreement through Parliament.

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May has been criticized by both sides of the debate for her handling of the implementation of the 2016 referendum, with Remain supporters accusing her of presiding over chaos, with pro-Brexit factions in her own Conservative Party claiming that she has kowtowed to Brussels and that her deal does not actually lead to Brexit being delivered.

“I’ll be voting against the withdrawal agreement because I don’t believe it delivers Brexit,” Conservative MP and top Brexiteer Jacob Rees-Mogg said on the BBC Tuesday.

Leavers hold up signs next to pro-European demonstrators protesting opposite the Houses of Parliament in London, Tuesday, Jan. 15, 2019. Britain's Prime Minister Theresa May is struggling to win support for her Brexit deal in Parliament. Lawmakers are due to vote on the agreement Tuesday, and all signs suggest they will reject it. (AP Photo/Frank Augstein)

The anger from the “Brexiteer” wing focuses primarily on the inclusion of a “backstop” -- a safety net that keeps Britain in a customs union with the E.U. in case no trade deal is made after March. It is intended to avoid a hard border between Ireland and Northern Ireland, but Brexiteers have pointed to the lack of a unilateral exit mechanism as evidence that the backstop will lead to Britain never actually leaving.

If May's agreement loses by more than 100 votes, it would likely renew calls from her own party for her to step down, and give impetus to the opposition Labour Party to put forward a motion of no-confidence -- a move that could eventually lead to a General Election. A Sky News analysis Tuesday suggested she could lose by as many as 226 votes -- which would be the largest defeat in House of Commons history, and catastrophic for May.

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Others who support Britain remaining in the E.U. have floated the idea of a second referendum, by which Brits would get a do-over on the 2016 referendum -- something May has rejected outright. That proposal has been condemned by many Brexit supporters as an effort to scrub out the 2016 referendum, what they say is a trend in Europe by which voters are made to vote again and again until they vote the "right" way.

In the face of withering criticism, May and her allies have been pushing back, hoping to keep the margin of defeat to a minimum.

May told a packed House of Commons ahead of the vote that "I believe we have have a duty to deliver on the choices of the British people." She also criticized Labour Party calls for a general election.

"At the end of a general election, the choices facing us will not have changed," she said.

Environment Secretary Michael Gove, who is a May supporter and also campaigned for Brexit in 2016, sought to rally Brexiteers to May’s side, using a "Game of Thrones" reference to warn that the damage would be significant.

“I think if we don't vote for the deal tonight, in the words of Jon Snow, 'winter is coming,’” he said on BBC's Radio 4, “I think if we don’t for vote the deal tonight, I think we will do damage to our democracy, by saying to people that we are not going to implement Brexit,” he said.

In the Commons on Tuesday, the bombastic Attorney General Geoffrey Cox gave a thundering hour-long speech, in which he boomed a defense of the withdrawal agreement and sought to counter arguments against it: “It is what the people voted for and we by adopting this withdrawal agreement, can give it to them.”

Warning about the dangers to Brexit and to the country of voting down May’s deal, Cox asked: “Do we opt for order or do we choose chaos?'

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To his own party, particularly the Brexit wing, he turned to the Tory benches and asked: “What are you playing at? What are you doing?”

A defeat also makes it unclear of the future for not only May, but also Brexit. Should the agreement fail, Britain is set to leave without a deal with the E.U., something that Remainers and some business groups have said would lead to chaos from an economic downturn to a lack of access to vital medicines as Britain’s ports clog up.

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Those on the right of the Tory Party have downplayed the risks of no deal, noting that Britain would revert to normal World Trade Organization terms and the benefits of leaving the E.U. would outweigh any difficulties.

“Cutting the costs of imports from outside the E.U., making our economy more competitive, is going to be extremely beneficial,” Jacob Rees Mogg told the BBC. “All the gloomsters, the prophets of doom, are the people who prophesied doom before and they’ve been wrong in all their earlier forecasts.”

May's supporters have argued that her way is the only way to avoid no-deal. In the face of one Labour MP who blasted Attorney General Cox for failing to acknowledge the dangers of “no deal,” Cox shot back: “She can rule out no-deal today, all she has to do is vote for this one.” He then accused the Labour Party of seeking to “drive this government onto the rocks, create the maximum chaos” and pave the way for an election.

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May told Parliament that the only way to avoid no deal was the vote for hers, and emphasized the importance of the decision in Britain's history.

"The time has now come for all of us to make a decision, a decision that will define our country for decades to come, a decision that will determine the future for our constituents, for their children and grandchildren, a decision each of us will have to justify and live with for many years to come," she said.