Next week, Britain’s politicians will gather in the House of Commons and cast what is likely to be the most important vote of their careers.

On December 11, MPs in the 650-seat chamber will get their chance to approve or reject Prime Minister Theresa May’s Brexit deal. Their decision will have far-reaching consequences.

So fragile is the British political scene, the outcome of the vote will usher in radical changes — the status quo is the least probable outcome.

A defeat for Mrs May would put her position in even more jeopardy. She has been facing calls to quit for weeks and is said to be close to reaching the number of no-confidence letters required to trigger a leadership spill.

But exactly what will happen to her if the deal is voted down is not certain. Aside from taking responsibility for the failure to get the deal through parliament and quitting, what happens to her will be decided by others.

She could go back to the European Union and ask for an improved deal, although they have already warned there would be no more concessions. Several countries, including France, believe the UK got too easy a deal in the first place, so it seems unlikely they will agree to another deal.

But a no deal would be a disaster for both parties, so it is possible she could return to Brussels and test their resolve not to renegotiate.

With Brexit day on March 29, 2019 rapidly approaching, what could happen next week?

NOT A GOOD START FOR MAY

Britain’s Parliament dealt Prime Minister Theresa May’s government two bruising defeats on Tuesday, even before politicians began an epic debate that will decide the fate of Mr May’s European Union divorce deal - and of her political career.

Opening five days of debate on the Brexit deal, Mrs May told Parliament that the British people had voted in 2016 to leave the EU, and it was the “duty of this Parliament to deliver on the result” of the referendum.

Despite her entreaties, the government appeared to be on a collision course with an increasingly assertive Parliament over the next steps in the UK’s exit.

Minutes before Mrs May rose to speak, politicians delivered a historic rebuke, finding her Conservative government in contempt of Parliament for refusing to publish the advice it had received from the country’s top law officer about the proposed terms of Brexit.

The reprimand, by 311 votes to 293, marks the first time a British government has been found in contempt of Parliament.

The PM lost three Commons votes - allowing MPs to take control of Brexit if her deal is defeated next Tuesday.

In a massive blow for the Prime Minister, MPs voted to hijack Brexit if her withdrawal agreement is defeated in the Commons - as is almost certain.

It means the Commons could order Mrs May to adopt a soft Brexit strategy - or even call a second referendum.

WILL SHE STAY OR WILL SHE GO?

Mrs May doesn’t have a majority in parliament and would be vulnerable to a no-confidence vote tabled by the opposition Labour Party. The party keeping her in power, the DUP (Democratic Unionist Party), are threatening to abandon her, which substantially raises the prospect she will lose that vote.

But even that is not clear cut. The DUP have previously not wanted to risk having Labour leader Jeremy Corbyn as prime minister, but now seem to view the Brexit deal as a greater threat than even him moving into 10 Downing St. Their continued support on confidence and supply cannot be assumed.

Oliver Wright, the policy editor at The Times, wrote yesterday Mrs May could bring this confrontation on and call a confidence vote herself. That is high-stakes stuff and would force the DUP to choose.

If they sided with her, she could continue as prime minister without the axe hanging over her. Lose, though, and she would have 14 days to try and cobble together a new majority. If that wasn’t possible, a general election would have to be called.

She could always call an election without a confidence vote. The Fixed Term Parliaments Act means a three-quarter majority would be needed for that to happen, but a snap election was achieved last year with little difficulty and Labour are pushing for a new election anyway.

The 2017 campaign was a disaster for Mrs May and the Conservatives, however, and that pain will be fresh in her mind.

Mr Corbyn is expected to call for her to resign immediately if the vote is lost. He will argue the Brexit vote is a de facto issue of confidence in the government as it is a major policy championed by the prime minister.

What she does could depend on how badly the vote is lost.

If it is rejected by more than 100 votes, she could quit. But so far she has shown remarkable resilience and an ability to fend off adversity to fight another day.

An unnamed MP told The Daily Telegraph Mrs May was “fed up” while another said she looked tired and appeared beaten by Brexit.

If she does go, the Conservative Party will hold an election for a new leader, a process that could take weeks. The Times suggested this week her deputy, David Lidington, could be nominated by Cabinet in an interim role. The Queen could appoint him on Mrs May’s recommendation with the aim of winning a Commons confidence vote under a new leader.

If not, then it’s election time.

WHAT STYLE BREXIT?

If she remains in power, Mrs May could also call a snap debate in parliament for MPs to try to determine the best way forward. But they are bitterly divided with each possible Brexit plan guaranteed to face big obstacles.

A soft Brexit — adopting a model that Norway currently has and staying in the single market — or holding a second Brexit referendum both don’t have the necessary support, and the option of leaving with no deal — the doomsday scenario that could cause major disruption to the economy — is favoured by even fewer MPs.

If a second referendum was held then Brexit would need to be delayed several months to allow the British people to have their say. Again.

If all other options failed, then Mrs May’s deal could be the only one left on the table.

Ministers are expected to try to push the deal though a second time if it is rejected and are hoping MPs are spooked by the likely stock market chaos and panic that would occur.

If Labour MPs fail at getting a new election and second referendum they will have to seriously consider voting for Mrs May’s deal to ward off crashing out of the EU with no deal.

But a second vote is not guaranteed.

All of this comes as a decision from the EU’s top court says the UK should be allowed to reverse Brexit. The fact it could be unilaterally revoked favours those who want to remain in the EU and could help those campaigning to thwart Brexit with a second referendum. But it could also encourage some wavering pro-Brexit MPs to vote for Mrs May’s deal in fear of no Brexit at all happening.

Whatever Brexit they end up with has to come into force by March 29 next year which is when the formal divorce begins and the 21-month transition period kicks in.

If that period ends without a trade deal being agreed, the dreaded “backstop” would come into force, potentially tying the UK into an indefinite customs union with the EU they would not be able to leave without EU permission.

During an interview with ITV’s This Morning, Mrs May called on politicians to “hold our nerve” and get the deal over the line — insisting it will make Britain better off in the long term.

And she confidently predicted she would still have a job in a fortnight.

“I will still have a job in two weeks’ time, and my job is making sure that we do what people have asked us to,” she said.

Asked if she was “knackered” by the Brexit drama, she replied: “It is a tough time, it’s been a difficult time, an awful lot of work has gone into this.

“The key point is, just keep focused on the endpoint. It’s about holding our nerve and getting this over the line.”

What happens once they get there is anyone’s guess.

andrew.koubaridis@news.com.au