Theresa May faces a leadership crisis after David Davis savaged the Government's approach to Brexit while dramatically quitting as the minister responsible for the UK's departure from the European Union.
His resignation was warmly welcomed by hardline Eurosceptics in the Tory ranks who were already expressing reservations about Mrs May's leadership after her Cabinet agreed a plan which would keep the UK closely tied to Brussels.
The Prime Minister now faces a stormy meeting with Tory MPs and peers in Parliament on Monday evening as she tries to keep her fragile administration together.
Mrs May had hoped that the Cabinet agreement secured on Friday at Chequers would help her deliver the "right Brexit" for the UK, with an offer to Brussels to share a "common rulebook" on goods and form a new UK-EU free trade area.
Mr Davis's departure just 48 hours after being part of the Cabinet that agreed to Mrs May's plans also triggered the resignation of departmental ally Steve Baker, while fellow Brexit minister Suella Braverman is also reported to have stepped down.
In his resignation letter, Mr Davis said the "current trend of policy and tactics" was making it look "less and less likely" that Brexit would deliver on the referendum result and the Tory commitments to leave the EU customs union and single market.
Mr Davis said "the general direction of policy will leave us in at best a weak negotiating position, and possibly an inescapable one".
The "common rulebook" plan "hands control of large swathes of our economy to the EU and is certainly not returning control of our laws in any real sense," he wrote to Mrs May.
"I am also unpersuaded that our negotiating approach will not just lead to further demands for concessions," he added.
The responsibility for leading the negotiations should now go to an "enthusiastic believer in your approach, and not merely a reluctant conscript", he said.
In her reply, Mrs May told him: "I do not agree with your characterisation of the policy we agreed on at Cabinet on Friday."
She said: "I am sorry that you have chosen to leave the Government when we have already made so much progress towards delivering a smooth and successful Brexit and when we are only eight months from the date set in law when the United Kingdom will leave the European Union."
Mr Davis's exit may embolden Brexiteer backbench MPs with concerns about Mrs May's leadership.
Arch-Brexiteer Jacob Rees-Mogg, leader of the powerful European Research Group faction within the Tory ranks, said his resignation should force Mrs May to reconsider her approach.
He told BBC Radio 5 Live: "These proposals will have to come to the House of Commons in legislation and the question is 'will they command support from Conservative MPs?'
"And I think without David Davis there, without his imprimatur, it will be very difficult for them to get the support of Conservative MPs and therefore the Prime Minister would be well advised to reconsider them."
Fellow Tory Brexiteer Peter Bone welcomed Mr Davis's resignation, saying it was "a principled and brave decision", while Andrea Jenkyns said Mr Davis's departure was "fantastic news" and hailed Mr Baker as "another courageous and principled MP".
Letters calling for a leadership contest have reportedly been submitted to the backbench 1922 Committee by some Conservatives over the weekend.
Tory MP Andrew Bridgen told the Press Association: "I can't support the offer which emerged at Chequers - I think it's a breach of the red lines, in fact the offer is so poor that I couldn't support it even if the EU were paying us for it."
Mrs May is expected to use a Commons statement to tell MPs that the strategy agreed on at Chequers is the "right Brexit" for Britain.
Mr Davis had come close to resigning before, but Mrs May must have hoped the danger of Cabinet resignations had passed after Friday's deal at her official country retreat.
Brexiteer Cabinet minister Michael Gove admitted the plan was not everything he had hoped for, but he was a "realist" and the Prime Minister's lack of a Commons majority meant the "parliamentary arithmetic" was a factor in deciding what could be adopted.
Foreign Secretary Boris Johnson backed the proposals at Chequers, despite claiming that defending the plans was like "polishing a turd" during the meeting.
In the Commons, Mrs May will acknowledge that there have been "robust views" around the Cabinet table and a "spirited national debate" since the 2016 referendum decision to leave the EU.
She will say: "Over that time, I have listened to every possible idea and every possible version of Brexit. This is the right Brexit."
She will tell MPs it was "the Brexit that is in our national interest" and "will deliver on the democratic decision of the British people".
The Prime Minister is expected to appoint a replacement for Mr Davis on Monday.
Labour leader Jeremy Corbyn said the Prime Minister "has no authority left and is incapable of delivering Brexit".
"With her Government in chaos, if she clings on, it's clear she's more interested in hanging on for her own sake than serving the people of our country," he said.
Copyright (c) Press Association Ltd. 2018, All Rights Reserved. Picture (c) Victoria Jones / PA Wire.