ITV News Political Correspondent Dan Hewitt explains the potential fallout above
MPs will vote on Theresa May’s Brexit deal on December 11 in what is the most important Parliamentary decision in decades.
After days of debates they will vote on the plan she agreed with Brussels after months of brutal talks, both with the EU and members of her own Government.
What happens if MPs back the prime minister?
If - against all odds - a majority back the PM then it’s all go.
The deal should be written into law before the March 29 exit deadline, which is when the 21-month transition period begins.
What happens if MPs reject the prime minister's deal?
There are several eventualities for Britain - and the PM - that could occur should the Commons reject her Withdrawal Agreement:
Theresa May could attempt some tweaks to the deal
The European Union have been adamant this is a take-it-or-leave-it deal and cannot be renegotiated.
But if faced with the threat of a calamitous no-deal Brexit, and following a narrow Commons defeat, Mrs May might fancy testing their resolve and seeing if she can win some cosmetic changes to appease enough MPs to win a second vote.
She could call it a day
Having made it this far and taken brickbats from all sides for months, and repeated assertions that she will not quit, it seems unlikely.
But this is 2018 and if the defeat is heavy enough it cannot be totally ruled out. However…
She could face a leadership challenge
Hardline Tory Brexiteers may have failed to muster the sending of enough letters of no confidence in the prime minister to backbench supremo Sir Graham Brady a fortnight ago and trigger a leadership battle.
But they are not the only unhappy ones and once the vote is over other players could make a move.
Move for a second referendum
Mrs May has said no, Labour says yes but only if it does not get a general election.
It would possibly require an extension of Article 50 to delay Brexit, with Tory former education secretary Justine Greening saying on Thursday that it could logistically be held by the end of May.
May calls a general election
The ultimate gamble for the prime minister, who has to hope that voters will, via the ballot box, back her plan.
But Labour has long called for an election believing that, after the 2017 election resulted in a hung parliament, it has the headway.
Labour could try to engineer an election
Under the Fixed Term Parliament Act, the opposition would have to win a vote of no confidence in the PM in the Commons and then hope the Conservatives could put together a Government which could win a second vote, in which case a general election would be called.
It would mean the DUP and a clutch of Tory rebels would have to side with Jeremy Corbyn, which seems unlikely.
Accept a No-deal Brexit
The warnings from institutions like the Bank of England, the CBI, and the Government’s own technical papers have been calamitous about the impact of leaving without a deal on March 29 – though some Brexiteers say much of this is an exaggeration.
But if everything else fails it’s possible that it could happen. Though a vast majority of MPs are adamant they'll do all they can to prevent it.
But when it comes to Brexit, anything is possible.