But what happens if Theresa May cannot convince her Commons colleagues to endorse the plan she has thrashed out with the Brussels bloc? On Tuesday, December 11, the House of Commons will seal not just the fate of the nation but also Mrs May. MPs will debate a motion tabled by the Government on its Withdrawal Agreement and accompanying Political Declaration – the terms of the UK’s departure from the EU.
But it is looking increasingly likely Mrs May will face a difficult job getting her agreement through Parliament.
With her unstable majority of just 13, only seven Tories need to rebel for her plan to be defeated.
Despite Mrs May insisting hers is “the only possible deal”, according to recent analysis by the BBC 81 Conservative MPs have said they object to the deal.
With Labour, the Liberal Democrats, the SNP and perhaps the DUP set to vote against the motion, too, the accord looks all but doomed.
Here are some of the possible options as to what happens next if the agreement is voted down.
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1. UK leaves without a deal
The default option would be to quit the EU bloc without a deal, trading on WTO rules.
Under EU law and the UK’s Withdrawal Act, “Brexit day” will take place at 11pm March 29, 2019.
From that day onwards, EU Treaties will no longer apply to the UK.
Under the Withdrawal Act, if Parliament rejects Mrs May’s deal ministers have up to 21 days to make a statement to the Commons about “how it proposes to proceed”.
The Government would then have seven days to bring a motion before the Commons, giving MPs the opportunity to voice their opinions on the issue.
In the no-deal scenario, MPs could not block the outcome if that is what the Government wanted.
The Government would have to put new legislation before Parliament and secure the approval of MPs if it did not want the UK to leave without a deal.
The clerk of the House of Commons, Sir David Natzler, told a committee of MPs last month: “There is no House procedure that can overcome statute. Statute is overturned by statute.”
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2. Commons urges May to go back to EU to renegotiate
A second option could be the House of Commons urges Mrs May to go back to Brussels to try and achieve a better deal.
The 27 could be persuaded to tweak the Political Declaration on the future relationship to meet the concerns of MPs.
Equally, the Prime Minister could try to make a second attempt at getting her deal through Parliament.
But Sir David Natzler said – in procedural terms – that would be impossible.
He said: “The words might be the same but the underlying reality would self-evidently be different.”
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3. General Election
The option favoured by Jeremy’s Corbyn’s Labour party would be a General Election.
But Dr Jack Simson Caird from the Bingham Centre for the Rule of Law said: “With the ticking clock of Article 50 it’s very difficult to see that this represents a solution to the problem of a deadlocked Parliament.”
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4. A second referendum or so-called ‘People’s Vote’
Finally, a second referendum on Brexit entirely – the preferred choice of those Remainer champions of the ‘People’s Vote’ campaign.
Theresa May is unequivocal in her rejection of the second referendum route.
And a ‘people’s vote’ could only happen if the Government brings forward legislation to hold one and a majority in the Commons supports it.
The rules for referendums are set out by the Political Parties, Elections & Referendums Act 2000.
The Electoral Commission’s recommendation is that there should be six months between the legislation being passed and referendum day.
These stipulations would leave no time at all to fit in a second vote before “Brexit day”.
A second referendum would, therefore, require the EU 27 to agree on a delay to Brexit.