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.

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.