LONDON — It’s the story dominating British news this week – the moment members of Parliament (MPs) finally cast their vote on Prime Minister Theresa May’s Brexit deal, determining the direction the UK will take as it leaves the European Union.

Will the threat of exiting with no deal scare enough MPs into backing May and her controversial plan for the Irish border, known as the “backstop”? Or will the European Research Group – a collection of ardent pro-Brexit MPs passionately opposed to May’s deal – be able to gather up enough support to topple the plan?

One way or another, it’s all people in the UK will be talking about. But how will the week actually pan out?

PA Wire/PA Images Prime Minister Theresa May's Brexit deal could be defeated in Parliament on Tuesday night.

After a gruelling five days of parliamentary debate on May’s Brexit deal, Tuesday evening will see MPs finally given the chance to decide whether to back the PM’s proposal on how the UK should leave the EU.

The so-called ‘meaningful vote’ comes a month later than originally expected after it was shelved by May back in December, who admitted at the time that her deal would have been “rejected by a significant margin”.

So the moment that MPs file into the House of Commons’ division lobbies will be a huge one for the PM – has she done enough to convince MPs, including those in her own party, to back her deal?

It won’t take long to find out. As little as 15 minutes later – after MPs have had their names recorded and counted by Commons officials – Speaker John Bercow will announce the result.

PA Archive/PA Images Bercow will announce the results of the meaningful vote

Here’s where things get really interesting. If May has remarkably managed to whip up a majority for her deal, the UK will leave the EU under the terms negotiated by the prime minister and her team – including the divisive Irish border backstop. (As long as it is passed by the European Parliament and Council.)

If she hasn’t… things get a bit more complicated.

On Wednesday night, the government suffered a significant defeat in the Commons after rebel Tory MPs joined forces with Labour to push through an amendment which means May will have just three sitting days to come back to the House with a new Brexit plan, instead of the previously agreed 21.

The amendment – put forward by Tory MP Dominic Grieve in a bid to avoid a no-deal Brexit – will give MPs the chance to vote on alternative Brexit plans – including a second referendum, a ‘managed’ no-deal or a ‘Norway-plus’ option.

If a new deal is agreed by Parliament, the government could go back to Brussels in an attempt to renegotiate a deal. But, given the fact that Brexit day – March 29 – is just weeks away, this would probably lead to an extension of Article 50, which is the legal process that sets forth a country’s exit from the EU.

Finally, if May loses the Brexit vote, Labour could trigger a no-confidence vote in the government, with leader Jeremy Corbyn announcing on Thursday it would trigger such a motion “at the moment we judge it to have the best chance of success”.

If MPs determine they have no confidence in the government, this in turn could trigger a general election.

Buckle in folks – it’s going to be a hell of a week.