Boris Johnson has appealed to MPs to get behind his deal in the face of a plan to delay Brexit.
The Prime Minister said the agreement he struck in Brussels represents “the best possible solution” ahead of a knife-edge vote on an extraordinary day in the House of Commons.
However Mr Johnson faces the prospect of having his plans to “get Brexit done” by 31 October derailed, with opposition parties threatening to withhold approval until legislation to implement the deal is in place.
The architect of the plan, former cabinet minister Sir Oliver Letwin, said it was simply an “insurance policy” to ensure the UK could not “crash out” of the EU without a deal on October 31.
This would almost certainly require the Prime Minister to request an extension regardless of whether his deal is successful.
With many of his fellow MPs who had the Tory whip withdrawn expected to back the amendment, the Government is facing a strong possibility of defeat.
If they lose, it is expected that ministers will simply order Conservative MPs to go home without voting on the main motion.
MPs would then likely come back early next week.
What are the numbers like?
The Prime Minister needs the support of 320 MPs to win a majority, assuming there are no abstentions.
With once-close allies the Democratic Unionist Party strongly opposed to the deal, Mr Johnson is left needing the backing of rebel Tory MPs and pro-Brexit Labour MPs to get the deal across the line.
As of early Saturday afternoon, at least 11 Labour MPs, had said they would vote in favour of Mr Johnson’s deal.
Labour Brexiteer Caroline Flint told MPs: "In voting for the amendment, we'll be forced, even if a deal is approved to seek an extension.
“The Benn Act had only one motivation and that was to delay Brexit and stop it."
The vote initially looked like it might hinge on whether Mr Johnson can win support from the Brexiteer faction of the Conservative Party after several members of the pro-Brexit Tory European Research Group indicated they may support the DUP’s stance on the deal.
However, the PM received an early boost when Steve Baker, the leader of the ERG, said he expected members to “overwhelmingly” to back the deal.
That means that if all 23 former Tory MPs - those who were expelled or quit the party in recent weeks - vote in favour of the deal, it could take Mr Johnson to 321 votes, which would be enough for a majority.
It is almost certain not all of them will - Sam Gyimah is one who is unlikely to - but the numbers remain very tight.
Johnson vs Corbyn
Speaking to MPs on Saturday, Mr Johnson urged MPs to back his deal saying he hopes today “is the moment we can finally” resolve Brexit.
He said: “The House will need no reminding that this is the second deal and the fourth vote, three-and-a-half years after the nation voted for Brexit.
“And during those years friendships have been strained, families divided and the attention of this House consumed by a single issue that has at times felt incapable of resolution.
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“But I hope that this is the moment when we can finally achieve that resolution and reconcile the instincts that compete within us.”
Responding to Mr Johnson, Labour leader Jeremy Corbyn said that “this Government can’t be trusted and these benches will not be duped”.
“It is not a good deal for our country and future generations who will feel the impact. It should be voted down,” he said.
“I totally understand the frustration and the fatigue across the country and in this House.
“But we simply cannot vote for a deal that is even worse than the one this House rejected three times.”