The prime minister is almost certain to suffer a defeat when the Commons votes next week. Various scenarios could play out …

It’s the evening of Tuesday 11 December. Despite the best efforts of the Tory whips, their arm-twisting has failed and Theresa May’s Brexit deal has been defeated in the Commons.

Labour MPs voted en masse against the deal. So have DUP MPs from Northern Ireland, while sufficient Tory MPs have rebelled to inflict a hugely damaging and historic defeat on their prime minister. After two-and-a-half years of tortuous negotiation, the whole process has hit the parliamentary buffers. So what happens next?

Scenario 1 May quits

After being humiliated by Brussels, rocked by waves of resignations and abandoned by many of her own MPs, May decides that she has finally had enough. She survived fluffing an election that many had expected to deliver a Tory landslide. She hung on after losing her voice during a “make or break” conference speech last year, and again after Boris Johnson and David Davis quit over her initial “Chequers” Brexit plan.

Even the departure of two more cabinet ministers over the deal on offer has failed to finish her off. But with parliament rejecting the only deal she believes is achievable, she sees no point carrying on. Given May’s previous resistance to stepping aside, this is an unlikely outcome.

Likelihood rating: Out of character for this stubborn PM. 1/5

Scenario 2 May renegotiates and tries again

Having lost the vote, May brings it back to the Commons having secured some cosmetic changes to the future relationship envisaged between the EU and Britain. However, the 585-page withdrawal agreement, the legal text that contains the “backstop” that Brexiters say would keep Britain tethered to the EU with no power to free itself, remains untouched. While the changes may not amount to much, Downing St hopes that with the clock ticking down to a disastrous no-deal Brexit, a sufficient number of MPs will step back from the brink and support the agreement.

Likelihood rating: Distinctly possible. 4/5

Scenario 3 Tory leadership challenge

While the initial attempt to topple May by the pro-Brexit European Research Group of Tories failed to gain enough support, another attempt could be launched once her deal has been voted down. The group of MPs who opposed her deal but stopped short of calling for a leadership election may change their mind after the parliamentary vote – especially if they think that May will make a second attempt to secure Commons backing for her agreement. There is a chance that 48 MPs will demand a vote of no confidence in May’s leadership, triggering a vote among all Tory MPs. However, May is more likely to win such a vote and stay in post.

Likelihood rating: Very possible, but a temporary diversion. 3/5

Scenario 4 No-confidence vote held in the government

With May’s Brexit deal defeated, Labour lays a motion of no confidence in the government in an attempt to force an election. An election is triggered if a no-confidence motion is passed and no one is able to form a government in the next fortnight. However, Labour would need the support of the DUP to pass such a vote – which currently looks uncertain. There is also a debate going on within Labour about the best time to table such a motion. It seems likely that Labour will try this – with very limited chances of success.

Likelihood rating: Labour likely to try - and fail. 4/5

Facebook Twitter Pinterest John McDonnell has said that a second referendum may be possible if Labour cannot force a general election. Photograph: Neil Hall/EPA

Scenario 5 Support emerges for a second referendum

With Labour having tried and failed to secure an election, the party then embraces a second referendum, despite internal splits over the issue. A sufficient number of Tory MPs also see it as the only way out of the impasse and a majority emerges for a second public vote. Theresa May would probably have to resign due to her opposition, and Brexit would have to be delayed beyond the end of March via the suspension of the article 50 process of EU departure. Cue a big row over the referendum’s wording and options.

Likelihood rating: Lots of hurdles to get there, but could emerge as only option. 3/5

Scenario 6 The Norway-plus option

MPs attempt to take matters into their own hands by rallying around the soft Norway-plus Brexit – which could well win a majority, as well as keeping Britain in the single market and customs union.

Problems are already emerging, though. Seeking the agreement of European Union countries to allow such a deal may well take years – while EU negotiators are likely to demand much tighter rules for Britain than those that are enjoyed by Norway. Ultimately, it would not alter the legal withdrawal agreement that so many MPs have expressed concerns about.

Likelihood rating: Hard to see what it resolves and may be undeliverable. 3/5

Scenario 7 No-deal Brexit

Labour does not want to leave the EU without a deal. Theresa May does not want to leave the EU without a deal. Senior MPs are trying to amend the vote to make clear that parliament opposes crashing out without a deal. But because a no-deal departure is the default position should no other solution emerge, it cannot be ruled out. Insiders in Whitehall and Brussels believe it is being underestimated as an outcome. However, faced with the cliff edge, the EU and Britain may opt to delay Brexit and kick the can down the road.

Likelihood rating: Cannot be dismissed. 2/5