On the eve of Tuesday's monumental vote in parliament on her withdrawal agreement -- forged from 18 months of gruelling negotiations with European leaders -- May is set to address factory workers in Stoke, a Brexit-backing city in central England.
The embattled leader, who is widely expected to lose the House of Commons vote by a wide margin, will make a final bid for support by warning Brexit-supporting MPs that they risk sabotaging the whole process, and reminding EU supporters of their democratic responsibilities.
"We all have a duty to implement the result of the referendum," she was to say, according to extracts released early.
"I ask MPs to consider the consequences of their actions on the faith of the British people in our democracy," May is expected to say, asking what the response would have been if parliament tried to take Britain out of the EU had Remain had won the 2016 vote.
She is also set to later make a statement to parliament, setting out reassurances from Brussels over contentious aspects of the deal, although there appears little prospect of her unveiling anything with legal force.
Leave-supporting MPs fear one provision in the deal for a "backstop", designed to prevent a hard border between the British province of Northern Ireland and the Republic of Ireland, would keep Britain indefinitely tied into a form of EU customs union.
'No confidence in the government'
Britain is set to leave the European Union on March 29 but, with less than 11 weeks left, has yet to finalise the terms of its departure.
May's deal agrees a 21-month transition period under current terms while the future relationship with the bloc is negotiated, but it has drawn steadfast opposition from both Brexiteers and Remainers.
The prime minister has said rejecting it will throw Britain into "uncharted territory" and put the country at risk of crashing out without an agreement, or even no Brexit at all.
The opposition Labour Party, which favours remaining in a permanent customs union with the EU, has suggested it will seek a no-confidence vote in the government if MPs throw out the plan.
The Observer newspaper reported Sunday that its lawmakers have been told it could be tabled "within hours" of that on Tuesday, with the confidence vote to be held the following day.
If the government loses a no-confidence motion, there will be a period of 14 days in which parties can seek to find an alternative working majority in parliament.
If they fail to do so, a general election would be called.
"We will table a motion of no confidence in the government at a time of our choosing, but it's going to be soon," Labour leader Jeremy Corbyn told the BBC on Sunday.
Corbyn conceded that, if the party won power, parliament would likely need to delay Brexit beyond March 29 so it could renegotiate the withdrawal agreement.
'A very British coup'
Lawmakers who believe the deal either leaves Britain too close or too distant from the bloc, fired ominous warning shots this week, voting to force the prime minister to quickly set out an alternative plan for Brexit if she loses the vote.
The Sunday Times said a group of senior cross-party backbench rebels are now plotting to change House of Commons rules to enable them to override government business if the deal falls.
Described as "a very British coup", the plan would see May lose control of parliamentary business to MPs, threatening her ability to govern, the newspaper said.
It said Downing Street was "extremely concerned" about the possibility, which could see lawmakers then delay Brexit through new legislation.
Conservative MP Nick Boles, who favours a Norway-style relationship which would keep Britain attached to the EU's single market, told BBC radio he was set to publish a bill that would allow MPs to frame a "compromise" Brexit deal.
"The European Union Withdrawal Number 2 Bill" would see parliament's Liaison Committee take a key role if the prime minister's withdrawal agreement is rejected by parliament.