THERESA May has staked her premiership on her Chequers deal for a smooth exit from the European Union.
But she faces fierce opposition from within her own party, and Labour plans to vote against it in the Commons. Here's what you need to know.
What is Theresa May's Chequers proposal?
After a marathon session of talks at Chequers on July 6, Theresa May and her Cabinet managed to hammer out a Brexit plan which she could take to the EU.
It would see the UK remain closely tied to Brussels on goods and agriculture, with the creation of a "common rulebook".
This rulebook could limit the UK's ability to strike trade deals with countries such as the US — for whom securing market access for American farmers would be a big prize.
When will it be voted on?
Mrs May hoped to get her deal rubberstamped by EU leaders, with some tweaks inevitable, before bringing it back to Parliament for approval.
But her plans were dealt a blow at crunch talks in Salzburg with other heads of government in September.
The PM was ambushed by EU bullies who dismissed her Chequers plan as out of hand.
Maltese and Czech leaders told Britain to hold a second referendum, employing the same tactic that the EU has used in Ireland and Denmark before.
It threw her plans into disarray as Tories on bother wings of the party openly called on her to ditch the plan.
Former Cabinet ministers David Davis and Boris Johnson, who resigned in protest at the proposal, called on Mrs may to "chuck Chequers" and seek a looser trade deal like Canada's.
But in a Panorama interview in September she said MPs had a simple choice between her Chequers plan or no deal.
She told the BBC current affairs programme: "I think that the alternative to that [the Chequers plan] will be not having a deal."
Once a deal has been agreed — if ever — MPs will be asked to approve it.
Will MPs vote against Chequers?
Opposition to the plan in the Conservative Party centres around the European Research Group of hard Brexit supporting MPs led by Jacob Rees-Mogg.
His voice had been among the loudest voicing their objection to the plan and he urged MPs “chuck Chequers”.
Up to 80 Tory MPs are prepared to vote against Theresa May's Chequers plan, warned Steve Baker, a former Brexit minister and ERG backer.
A group of about 50 Tory MPs have met to discuss how and when they could force Mrs May out of her job, the BBC reported.
Boris Johnson, widely seen as a leadership contender, said Theresa's May had "wrapped a suicide vest" around the British constitution and "handed the detonator" to Brussels.
The former Foreign Secretary later claimed Mrs May's disastrous plans would mean Northern Ireland was "annexed" by Brussels.
And at the Tory Party Conference on October 2, he claimed the Chequers proposals would force Britain to accept Brussels laws forever and stop us cutting trade deals.
Along with former Brexit secretary David Davis, Mr Johnson resigned in protest following the Chequers meeting.
Several other MPs also quit their ministerial posts over the issue, including Steve Baker, Maria Caulfield, Ben Bradley and Robert Courts.
What have David Davis and Penny Mordaunt said?
In October 2018 former Brexit Secretary David Davis wrote to Tory MPs to warn them to ditch her Chequers plan “immediately” or be wiped out, as another ex-Minister said the party was “starting to resemble the closing scene of a Tarantino movie”.
Mr Davis repeated his plea for the UK to "chuck Chequers" and instead seek a looser free trade deal with Brussels like Canada - quickly branded a “delusion” by his successor Dominic Raab.
Aid Secretary Ms Mordaunt publicly refused to back the Chequers deal, as she repeatedly dodged questions over whether she backed the PM’s blueprint.
She insisted she “fully supported” Mrs May, but said her backing was conditional, adding: “All I would say is that we don't know where this is going to end up. We are at a critical moment now."
The Soft Brexit agreement in 6 bullet points
THERESA May’s UK-Free Trade Area:
- “Common rulebook” would keep British producers bound by EU rules on goods - including farmers.
- Parliament would oversee these rules - but deciding not to abide by them would have “consequences”.
- Joint UK-EU “Joint Committee” to oversee and rule on disputes but these would be settled based on more than 40 years of EU laws.
- Britain to effectively stay in the EU’s customs union - described as a “combined customs territory” - to avoid hard border with Ireland.
- Britain to be responsible for collecting EU tariffs and implementing EU trade policy for goods passing through the UK.
- Britain to leave EU rules for services - with banks losing crucial EU passporting rights that allows them to sell their services across Europe.
Why has Labour planned to vote against it?
Labour MPs have threatened to vote against any deal based on Theresa May's Chequers plan.
At the Labour party conference on September 25, shadow Brexit secretary Sir Keir Starmer said that the plans look set to fail the six tests he set out for any deal with Brussels,
Labour members will then debate and vote on whether all options - including a referendum - should remain open.
Their policy is to force an election if MPs are deadlocked over Brexit.
But members have managed to get a debate on a fresh referendum on the agenda at the conference in Liverpool.
The motion says: "If we cannot get a general election, Labour must support all options remaining on the table, including campaigning for a public vote."
Previously, the party said it will vote down any Brexit deal brought back from Brussels by Theresa May, according to shadow Foreign Secretary Emily Thornberry.
The Corbyn ally said the party will oppose it to try to force an election by Christmas.
Speaking to the she said a deal which meets her party’s tests was “not going to happen”, and therefore the Prime Minister would be forced to quit.
Without the support of the opposition party, it would need just a handful of Tory rebels to vote against her to see it defeated.
What has Jeremy Corbyn said?
Speaking at the party conference on September 26, the Labour leader vowed he would become Prime Minister within a year in his speech to the party conference.
The Labour boss claimed getting a Brexit deal in Brussels would be a "piece of cake".
Vowing to vote against Theresa May's deal when it comes to the Commons, he said his Brexit Secretary Keir Starmer would have more luck negotiating with Brussels.
Mr Corbyn said: "Theresa May used to say that ‘no deal is better than a bad deal’.
"Yet now, after two years of botched negotiations she is threatening the country with just that choice: a bad deal or no deal.
"That is a threat to our whole economy, especially our manufacturing industry and to tens of thousands of skilled jobs here in Britain."
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And he again repeated calls for a General Election so Labour can try and take No 10.
He said if the PM doesn't get a good Brexit deal "you need to make way for a party that can".
Tories have claimed some Labour backbenchers will defy their leader and vote with Mrs May on Brexit because they don't want Mr Corbyn to become PM.
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