When MPs adjourned for Christmas on Thursday, after what the deputy speaker Nigel Evans described as an “awful year”, they were all aware that their festive break might be interrupted at any moment. If Boris Johnson can strike a free trade deal with Brussels in the next few days, legislation to pass it into UK law will be put to a Commons vote, if at all possible before 31 January and MPs will be summoned back. Four and a half years on from the referendum, the final vote will effectively mark the end of the Brexit process. While any deal short of a complete national humiliation will almost certainly pass, deciding how to vote will not be easy for many elected members, or for opposition party leaders. So where do the main parties and their MPs now stand, as they prepare to conclude the most divisive debate in recent UK political history?
Conservatives
Boris Johnson sees delivering Brexit as the defining act of his political career. But some of his hardline pro-Brexit MPs will only accept pure Brexit, meaning no concessions to the EU. To get a deal with Brussels, however, Johnson will have to make some compromises on issues such as EU access to UK fishing waters, and UK compliance with rules governing the single market to which we want to continue to have access. It is these compromises that the hardline pro-Brexit European Research Group, which has around 70 Tory MPs as members, will be looking out for. If they believe significant ground has been given, some or all of this group will refuse to back the deal.
MPs like the former cabinet minister John Redwood, who has often made the case that a no-deal outcome would be quite acceptable, could even vote against. For veteran sceptics like Bill Cash and Bernard Jenkin, getting Brexit done will be the culmination of decades of toil. But they will not be happy if it is a fudge of the sort that allows Nigel Farage to declare it is not a real Brexit at all. A big Tory revolt on his defining policy is something Johnson is desperate to avoid.

Labour
Labour’s leader Keir Starmer was a prominent Remainer and was at the forefront of those pushing for a second referendum. But having won the leadership, and after Johnson comfortably won last December’s general election, Starmer has been determined to move on, to the point of hardly mentioning Brexit at all in recent months. Conscious that millions of traditional Labour supporters voted to leave the EU, Starmer now wants his MPs to support any reasonable deal. Most will fall into line. But some ardent Remainers on both the right (Ben Bradshaw, perhaps) and the left (Diane Abbott) will find it difficult to back any form of Brexit, let alone Johnson’s Brexit. Some leftwingers may simply recoil from supporting a deal because it was the work of the Tories. But any Labour rebellion is likely to be limited because the only alternative to a last-minute deal is far worse: a last-minute no-deal.
The SNP
The SNP is strongly against Brexit and a clear majority of Scots voted to remain in the EU in the referendum. So Nicola Sturgeon and her 47 Westminster MPs believe they have a mandate to reject it. The official line from the SNP is that they would look carefully at any deal brought back by Johnson before deciding what to do. But as Sturgeon pushes towards another independence referendum and with the May 2021 Holyrood elections approaching, which will she hopes will be a big step on the road, it is hard to see how the SNP could ever back a Tory Brexit deal.
The Lib Dems
Like the SNP, the Liberal Democrats – who now have only 11 MPs at Westminster – say they will take a look at the deal before deciding. The party’s leader Ed Davey has said he will not be campaigning to rejoin the EU in the near future – after the party’s “revoke” message backfired badly at the last election, seen even by many party members as undemocratic. That said, it is very hard to see how a party whose members and MPs are overwhelmingly pro-EU and whose internationalism is at the heart of its policy agenda, could ever back a Johnson deal.
The DUP
The eight Westminster MPs in this Northern Irish party, which held the balance of power when Theresa May was prime minister, are not in the best of moods about Brexit. The party does not like the Northern Ireland protocol agreed as part of the withdrawal agreement. In order to ensure trade keeps flowing, the protocol keeps Northern Ireland in the EU’s single market for goods and means it will apply EU customs rules at its ports. As such, the DUP object as it treats Northern Ireland as separate from the rest of the UK. That is not popular among its supporters. So there is no guarantee at all that the DUP will back Johnson on any deal he puts to the Commons.