British MPs will vote on various options for leaving the European Union (EU) on Wednesday, a process that looks to have jolted opponents to Prime Minister Theresa May's Brexit deal to switch sides ahead of a likely meaningful vote by the end of this week.

The indicative votes are widely expected to point towards a preference in parliament for a softer Brexit or second referendum. Hardline members of May's Conservative Party have been holding out against her deal, but are even more strongly opposed to such alternatives.

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What are the Brexit options?

A softer Brexit – or an election

The push for indicative votes, a process which involved MPs taking control of the parliamentary agenda from the government and was strongly opposed by the prime minister, has effectively resuscitated her twice-defeated deal.  

Support from members of the European Research Group (ERG), the hardline anti-EU faction within the Conservatives, will come at a cost, however.   

Boris Johnson, the former foreign secretary and London mayor, is one of several ERG members to indicate that the price of his vote would be the resignation of the prime minister, who will be under pressure to put a timetable on her departure at a meeting with Conservative MPs on Wednesday afternoon.  

Johnson said on Tuesday evening that the current agreement with the EU was a "terrible deal," but indicated he would be prepared to back it so long as "the second phase of the negotiations will be different from the first.”

A promise by May to stand down before a second stage of Brexit talks – about the future relationship between the UK and EU – is likely to unlock a chunk votes from the ERG, though a handful would likely still oppose.

Whether it's enough to push the deal over the line will depend on the stance of the Democratic Unionists (DUP), the Northern Irish party whose support gives Conservatives a majority in parliament.

DUP Brexit spokesman Sammy Wilson on Tuesday said he would prefer a Brexit delay to backing May's deal, but the party is still in negotiations with the government and could change course at the last minute. Several ERG members have said they will vote for May's deal if the DUP do the same.

16 indicative options have been proposed, and Speaker John Bercow will decide which will be debated and voted on. May's deal is not expected to be one of the choices on Wednesday.

Importantly, it remains unclear whether MPs will be instructed to vote along party lines or with their conscience when alternatives are put to them.  

The opposition Labour Party has indicated it could be prepared to put its weight behind the Common Market 2.0 proposal – remaining in the single market and a customs union – and a ratification referendum, as well as its own plan for customs union membership. 

The decision for the Conservatives is more difficult. A free vote would allow ministers to vote against government policy, a whipped vote would likely lead to further resignations – adding to the three ministers who resigned on Monday to back indicative votes.  

The votes will not necessarily bring a majority for any option and are non-binding, though MPs also control the parliamentary agenda on Monday and may use the time to whittle down the options to a single preference.

If May's deal is approved in a meaningful vote this week, the indicative votes would become obsolete. If it's not voted on or rejected again, a softer Brexit – or even a general election – would be possible as Britain heads into uncharted territory.