The meaningful vote on Theresa May’s Brexit deal begins at 7pm on Tuesday night but MPs will have their say on a series of amendments first.
The Speaker will announce this morning which he has picked. The limit of six has been lifted.
Each amendment to the vote – known as a division – can last about 15 minutes.
Downing Street is preparing for a big rebellion with sources suggesting more than 100 Tory MPs could vote against.
But the big unknown is what happens next.
Theresa May’s Plan B
Whatever the result the PM is expected to make a statement straight after the result setting out what she plans to do next.
There are suggestions the Government could ask MPs to vote on the same deal again at a later date.
No 10 hopes that the pressure of a fast approaching Brexit day and a lack of an alternative plan will focus MPs’ minds.
Parliamentary rules usually prevent the Government asking MPs to vote on the same question but if it tweaks the wording it could get away with it.
Brussels sources suggest they want to see how the vote goes before they offer more compromises.
May’s deal – but with guarantees
Downing Street has indicated it will accept one amendment, proposed by Tory MP Hugo Swire.
This supports the PM’s deal but would give MPs a future vote to approve the implementation of the Northern Ireland backstop.
It includes six conditions on the “insurance policy” to avoid a hard border, after the PM said Government was looking at ways to make sure the backstop has “democratic legitimacy”.
But questions remain over whether these commitments would breach the UK’s international obligations to the EU.
Tory MPs Andrew Murrison and Sir Edward Leigh have tabled other amendments which would put a time limit on the backstop.
Their plan is to reduce the scale of a Government defeat, although the PM has conceded that Brussels wouldn’t go for it.
MPs take control
Three Tory former ministers led by Nick Boles have said a senior panel of MPs – the liaison committee – should be given responsibility to come up with their own compromise deal.
He has denied the move was a “coup” but admitted it would see power handed to the liaison committee, chaired by second referendum backer Sarah Wollaston, to find a way forward.
But Wollaston has complained that the liaison committee was not consulted by the plan and No 10 has warned against it.
What time is the Brexit vote? Parliament to vote on Theresa May’s EU deal today
Jeremy Corbyn’s plan
The Labour frontbench amendment rejects the PM’s deal because it fails to meet its “six tests” on Brexit.
The party has also rejected leaving without a deal and has promised to “pursue every option” to avoid either of those outcomes.
However, Mr Corbyn and his top team have repeatedly stated they want to force a general election, and would table a no confidence vote in the Government at the moment they believe they are most likely to win.
Several shadow cabinet ministers have suggested this could be immediately after a defeat, although without the DUP abstaining they are unlikely to win.
May’s deal – and no Brexit kicked out
Senior Labour MP Hilary Benn has tabled an amendment that both rejects the PM’s plan and also the UK crashing out of the EU without a deal.
The chair of the Brexit committee has won cross-party support from MPs campaigning for a second referendum, including leading Tory rebel Dominic Grieve, SNP MPs and senior Labour backbenchers like Yvette Cooper.
This boosts the amendment’s chances of being selected, although Mr Benn is said to have come under pressure to withdraw as some Tory MPs oppose leaving without a deal, but still want to support the PM.
The SNP and Plaid Cymru have warned that the PM’s Brexit deal would be damaging for Scotland, Wales and the UK as a whole.
They argue that the UK’s departure from the EU should be delayed until another withdrawal deal is agreed with the UK.
This would involve the Government delaying or revoking article 50 to delay Brexit Day beyond March 29, something it would be unwilling to do unless its hand was forced by MPs.
Any delay would also require the agreement of the EU, which has made it clear it would not agree just for more negotiations.
The Lib Dems have called on the Government to prepare for a “People’s Vote” in which the public would get a fresh public vote.
But the official People’s Vote campaign called the move “clearly unhelpful” as it would come too soon to have any realistic hope of success.
The amendment does not have cross-party support which suggests it may not be picked by the Speaker. Many second referendum campaigners believe that the option should be put on the table as last resort – and once every other option has been defeated – if it is to get the backing of enough MPs.
Workers rights protections
This amendment, tabled by Labour backbencher John Mann, supports the PM’s deal on condition the government maintains standards in employment, environmental protection and health and safety.
It has the backing of six Labour MPs but the unions and the party leadership have opposed it, arguing that it would not be legally binding.
Theresa May met with a handful of Labour MPs over Christmas, most who represent Leave-voting constituencies, in a bid to win their support for her deal.
So far four Labour MPs have said they will vote for the Government’s Brexit plan.