Theresa May's resolve will be tested like never before this week, as MPs devote the next two days to debating the key Brexit bill which will shape the UK's future relationship with the European Union.
Ministers want to overturn or alter 14 out of 15 amendments to the bill proposed by the House of Lords in mid-May.
During what is likely to be a highly-charged appearance before the backbench Conservative 1922 Committee on Monday evening, Mrs May will highlight that although the bill is largely a technical measure, the way her party votes will send an important signal to the country.
After months of debating the detail of the legislation that will trigger United Kingdom withdrawal from the European Union, the House of Commons will stage crucial votes on Tuesday and Wednesday that will decide her fate.
May is struggling to unite not only her party but her top team of ministers over how to leave the European Union, particularly over the future customs arrangements which have pitted those wanting closer ties with the European Union against others who demand a clean break.
Some pro-EU Tories were reported to be backing away from voting against government, over fears that a defeat could prompt a leadership contest and see Mrs May replaced by a far more hard-line Brexiteer.
But ministers are taking nothing for granted, with whips working hard over the weekend to convince MPs.
Labour are urging Tory rebels to side with them in the Commons on Tuesday and Wednesday with Labour's Sir Keir Starmer saying Tory rebels had a "real chance to change the course of the Brexit negotiations".
He dismissed claims a government defeat could lead to a general election where Jeremy Corbyn could take power. She had nearly lost a general election she never needed to call, squandering her Conservative Party's overall majority and forcing her to rely on the support of the smaller Democratic Unionist Party.
Rebel MPs have suggested they have sufficient numbers to threaten the government and want more concessions.
But with only 10 months left before Britain is due to leave, her government is under pressure from European Union negotiators, businesses wanting clarity, and from many in the country to start taking decisions on its preferred future trading ties.
Others, such as veteran Conservative MP Ken Clarke, however, have said the prime minister is being "undermined" by her ministers and needs to be "rescued".
Prime Minister Theresa May will urge her Conservative Party on Monday to show unity when parliament votes on changes to her Brexit blueprint, a potential showdown that could reshape her approach to Britain's departure from the EU.
Housing minister Dominic Raab said he was "reasonably confident" the government, which will have the support of a handful of pro-Brexit Labour MPs and the 10 Democratic Unionist MPs, would prevail.
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