As the Brexit deadline looms and pressure rises, parliamentary mathematics has become increasingly difficult to predict, ahead of Tuesday's crucial vote to decide whether to accept Prime Minister Theresa May's deal.
Here is the current political lay of the land.
- May loyalists -
About a third of MPs still say the deal May struck with Brussels was the best Britain could have hoped for when its voters shocked Europe by deciding to leave in 2016.
Some of them are paid government members and have no real choice. Others just want to see a deal done and the nagging uncertainties vanquished.
May hopes that more MPs join them, under the joint pressures of time and of fear that their version of a perfect Brexit will be subverted by those who want no deal or no Brexit at all.
- Backstop -
The key issue in deciding Tuesday's vote appears to be the deal's "backstop" solution for keeping the border open between Northern Ireland and EU member Ireland.
May's minority government relies on the votes of the DUP, a small Northern Irish party that supports Brexit but bitterly opposes the "backstop".
Voting against the deal in January, DUP leader Arlene Foster said the backstop was "toxic" and "would cause the break up of the United Kingdom".
They are joined by a band of veteran eurosceptics in May's Conservative party who say the stop-gap arrangement would tie Britain into an open-ended customs union with the EU, turning it into a "vassal state."
But there are signs that some of their opposition may be softening and it remains to be seen whether the agreement struck between Britain and the EU in Strasbourg late on Monday could sway them.
- No deal -
Some opponents of May's deal think London's best bet is to make a clean break with Brussels without any binding deal, allowing Britain to immediately set lower tariffs for trade outside the EU and finalise deals with the rest of the world.
They champion free-trade rules and see government warnings about border chaos and an economic recession as scaremongering.
If the deal is rejected on Tuesday, they will get their chance to vote in favour of a no-deal Brexit in another parliamentary vote set to be held on Wednesday.
- No no-deal -
But there is a solid majority in parliament in support of preventing Britain leaving the EU without a deal.
This group spans the political divide and includes finance minister Philip Hammond and top members of the main opposition Labour party.
Any vote on a no-deal Brexit is likely to be rejected.
This would trigger another vote Thursday on whether to ask the EU to extend the departure date, which would probably command a majority.
The "no no-dealers" are mostly centrists who have either long opposed Brexit or grown frustrated with May's inability to win over critics at home and abroad.
But the MPs will also have to weigh up public opinion, which has shown some signs of becoming increasingly in favour of a no-deal Brexit.
- Second referendum -
Calls for a second Brexit referendum rang out almost as soon as the Leave camp won the first vote, but the controversial option doesn't appear to have public support, according to polls, or a majority in parliament.
Its proponents argue that May's deal doesn't deliver what was advertised during the campaign and that Leave voters didn't know what they were voting for.
Some of its main proponents, including former Conservative MP Anna Soubry and former Labour MP Chuka Umunna, took drastic action last month, leaving their parties to join an independent group, with Brexit loyalties trumping party.
The move jolted Labour into backing a second vote, despite the long-stated opposition of veteran eurosceptic leader Jeremy Corbyn, fearful of losing more of his pro-EU MPs.
Long-time supporters include the Scottish and Welsh nationalist parties and the pro-EU Liberal Democrats.
May calls the idea undemocratic. There is also no agreement about what question another ballot would ask -- or what would happen if Brexit won again.