Parliament to vote on May's Brexit deal: what happens next?

Theresa May is facing the reckoning of her premiership on Tuesday, when she is expected to put her negotiated Brexit deal in front of her mutinous MPs. Here’s what could happen in that fraught 24 hours.

The government loses the vote by more than 100 MPs

The numbers who say they will vote against the prime minister’s deal are going up rather than down. Over the weekend a handful more have added to the tally, including the former chief whip Andrew Mitchell and the ministerial aide Will Quince.

That would be more than half of all Conservative backbenchers – those not on the government payroll. Such a defeat would be unprecedented in recent political times and a sign that Tory whips had little effect.

Faced with such a defeat, May would need to decide whether to resign or pledge to seek changes from Brussels. Under the terms of the EU Withdrawal Act, she would need to make a statement to the Commons within 21 days – although in practice it would probably take place the following day. Labour may also decide this is the moment to attempt a vote of no confidence in the government or Tory MPs could trigger a confidence vote in May.

The government loses by about 30 to 50 MPs

It is hard to see the prime minister managing to reduce the number of Tory rebels below this number. It is roughly the number of MPs who have either signed no-confidence letters in May’s leadership or resigned from the government to vote against the deal. It would still represent a staggering defeat, but the numbers that have vowed to vote against her deal are so vast that reducing it by half begins to look like an achievement.

Under those circumstances, May might be able to keep her job and pledge to seek some cosmetic changes in Brussels or some additional written assurances – or offer some concessions to Labour. It is possible then that she may survive long enough to put the deal again to parliament, perhaps with the hope of additional Labour support. That in turn could also lead to Brexiters forcing a vote of no confidence in May.

The government wins the vote in parliament

Highly unlikely, but still technically a possibility. Downing Street remains insistent that this is plan A and there is no plan B beyond it. One of the tactics whips have used to convince MPs is to insist this is the final decision day and that only chaos lies beyond it.

Other possibilities include a surprise new amendment or written guarantee on some aspects of the backstop from Brussels that assuages Tory fears. That seems extraordinarily far-fetched at this stage in the game.

Even if May wins the vote, she is not out of the woods. Brexiters have threatened to amend and block the legislation needed to enact the withdrawal agreement and the DUP has said its confidence and supply arrangement with the government will be over if the deal passes.

Theresa May quits

The prime minister resigns after a humiliating defeat. Many MPs believe she will have to go if she loses by more than 100 votes. An interim prime minister would have to be chosen while the Tory party plans a leadership contest.

PM goes cap in hand back to Brussels

May begs Michel Barnier, the European Union’s chief Brexit negotiator, left, to go the extra mile and reopen the talks. She asks for concessions over the Irish backstop, and then puts whatever she can secure to a second vote in the Commons.

May promotes the Norway option, floated by Amber Rudd and others

Plenty of Conservative and Labour MPs would be happy to see a soft-Brexit, Norway-style solution that keeps Britain in the single market, as suggested by Amber Rudd, the work and pensions secretary. Although she has previously rubbished the idea, May could do a U-turn and try to sell it as a compromise to avoid the disaster of no deal.

May caves in to calls for a second referendum

With her deal ditched, and if “no deal” is also ruled out by parliament, May’s least worst option could be to go back to the people. Many Tory MPs are pushing her to do so. If Labour officially backs the idea, a second referendum –as suggested by Keir Starmer, the shadow Brexit secretary – could happen.

May or her successor accepts defeat and agrees to a no-deal Brexit

If parliament cannot agree on what kind of exit from the European Union it wants, and if there is no majority for a second referendum, Britain hurtles towards a no-deal departure on 29 March 2019. A hardcore group of Brexiters led by Boris Johnson and Jacob Rees-Mogg would rather accept trading with Europe on basic World Trade Organisation terms than May’s deal or any form of soft Brexit.

Brexit is dropped without a second referendum

If there is no agreement on anything, and “no deal” has been blocked off as an option by parliament, the other choice available is no Brexit. May or whoever is in charge could form a cross-party government of national unity, revoke Article 50 and call the whole thing off.

May pulls the vote in parliament

The nuclear option remains that the prime minister could decide that there is nothing to be gained in allowing the deal to be put to MPs in its current form. It is unclear exactly how that could be achieved as MPs have already approved the House of Commons’ business motion to hold the vote on Tuesday. A minister could simply decide to talk beyond the time limit so a vote is not held, but would be likely to cause uproar.

If May decides it is a risk worth taking, and No 10 insists she will not, she may head to the EU council summit at the end of the week to try to seek some tweaks or concessions, or allow the clock to tick down even longer so MPs begin to feel the heat of a potential no deal. Both are very high risk strategies.