The prime minister is due to hold a special Brexit-focused Cabinet meeting on Tuesday morning knowing that her next move in negotiations could trigger mass resignations and risk the collapse of her government.
However, seven senior members of her cabinet met on Monday night in an apparent plot to undermine her plans.
Tuesday's meeting was originally scheduled for her Cabinet ministers to sign off a Brexit divorce deal with the EU.
However, a fraught weekend in Brussels culminating in UK Brexit Secretary Dominic Raab walking away from the negotiating table, means a deal won't be signed off until November - if there is a deal at all.
An EU Commission source told Business Insider on Monday that they were more pessimistic than ever about the prospect of the UK being able to agree a deal before Brexit.
"The deal is definitely going to be pushed back to November, if it happens at all," the source said.
Hopes of an imminent deal were shot down on Sunday after the UK government refused to accept the EU's demands to keep Northern Ireland in the customs union and single market if a new customs arrangement is not secured by the end of the two year Brexit transition period. The so-called backstop is designed to prevent a hard border on the island of Ireland after Brexit.
However, while May's refusal to make more concessions to the EU in talks delayed a revolt in Westminster, the prime minister's leadership remains precarious, with senior Cabinet ministers last night openly meeting to discuss how to undermine her plans.
On Monday evening, arch Brexiteer Andrea Leadsom hosted seven other Cabinet ministers in her office, where they ate pizza and discussed what to do next.
The attendees were Environment Secretary Michael Gove, Transport Secretary Chris Grayling, Chief Secretary to the Treasury Liz Truss, Foreign Secretary Jeremy Hunt, Attorney General Geoffrey Cox, International Development Secretary Penny Mordaunt, and perhaps most worrying for the prime minister, Brexit Secretary Dominic Raab.
Business Insider reported last week that Leadsom, Mordaunt and Work and Pensions Secretary Esther McVey were all prepared to quit Cabinet if the prime minister did not change her plans for the Brexit backstop.
A Cabinet source said on Monday that despite May's refusal to give in to EU demands, ministers were very worried by what she said to the House of Commons earlier that day, telling BI: "Pizza club should be interesting tonight."
May reassured MPs on Monday that she would not accept the EU's demand that the backstop plan for the UK to stay in the customs union after Brexit to be indefinite. However, she dodged questions from pro-Brexit MPs like Boris Johnson and Iain Duncan Smith, who asked her whether the backstop would have a fixed end date.
The mood among pro-Brexit Conservative was summed up by Simon Clark, who told the prime minister directly that she had as "failed to reassure" MPs that the UK will definitely leave the customs union by December 2020, amid fears that the UK could be wedded to the EU's customs arrangements for years and years to come.
It was a gruelling House of Commons experience for May, who was grilled by all sides of the Brexit argument and reminded of how many factions she must please to have a chance of getting a Brexit deal through Parliament.
The prime minister failed to reassure MPs from the Democratic Unionist Party that there'd be no new regulatory checks between Northern Ireland and the rest of the UK after Brexit, and received a kicking from numerous pro-EU MPs, including up to 10 MPs who urged May to back another referendum.
Multiple reports suggest Cabinet resignations have been put on hold for at least another day with restless ministers prepared to give Prime Minister May more time to satisfy their demands.
However, with the EU incredibly unlikely to budge on the backstop issue, and the prospect of a chaotic no deal looming, May soon could be forced to accept their demands, which would almost certainly be the catalyst for a government implosion.
Also from Business Insider South Africa: