DAVID Davis has dramatically resigned as Brexit Secretary in a massive blow to Theresa May.

He quit his post just days after the Prime Minister triumphantly sealed Cabinet agreement for her Chequers compromise plan, which plots a softer Brexit course but which has enraged Brexiteers as a “complete capitulation” to Brussels.

The development will rock Westminster and threw up the possibility of more resignations with eyes on Boris Johnson, the Foreign Secretary.

The move will also open up the possibility of a direct threat to the Prime Minister’s own position as she seeks to fill at least one major hole in her wavering Cabinet. The reaction from Brussels later today will be one of disbelief and dismay.

As news broke just before midnight, Ian Lavery, the Labour Chairman, said: “This is absolute chaos and Theresa May has no authority left.

“The Prime Minister is in office but not in power. She cannot deliver Brexit and our country is at a complete standstill, while the Tories indulge in their leadership tussling.

“We can’t go on like this. Britain needs a functioning Government.”

His Labour colleague Seema Malhotra, who sits on the Commons Brexit Committee, tweeted: "Will there be a domino effect?

"It's now not inconceivable that May is gone within days or weeks, the Tories are plunged into disarray and a general election called."

Fellow Labour backbencher Mary Creagh also took to social media, tweeting: "David Davis doesn't even give May the courtesy of resigning during the day. Leadership contest imminent..."

She added: "Johnson & Grayling only 2 Leavers who have not backed May publicly this w/end. Tick tock."

Brexiteers made clear their support for Mr Davis’s bolt from the blue departure.

Tory MP Peter Bone supported Mr Davis's decision to quit. He said: "David Davis has done the right thing, a principled and brave decision. The PM's proposals for a Brexit in name only are not acceptable."

Conservative MP Andrea Jenkyns, who quit a junior Government role earlier this year to "fight for Brexit" and has threatened to vote against Mrs May's Brexit plan, tweeted her approval of Mr Davis' resignation.

"Fantastic news. Well done David Davis for having the principle and guts to resign. I take my hat off to you. We need to make sure this is now a game changer for #Brexit."

Tory colleague Henry Smith appeared also to support Mr Davis' stance, tweeting: "Last year I stood on an election promise to deliver the British people's 2016 referendum decision [by the largest number in our democratic history] to leave the EU, ECJ, Customs Union, Single Market and open border access. I work for my constituents and country first, and always."

Mr Davis’s shock resignation comes as Mrs May faces MPs and then a potentially stormy meeting of Tory MPs and peers later today.

It follows calls by Cabinet members for angered Tory Brexiteers not to launch a direct challenge to Mrs May’s leadership as the PM will tell them today that her Chequers plan is the “right Brexit for Britain”.

David Mundell called on colleagues to unite behind Mrs May, telling The Herald: “Rather than focusing on ourselves, we need to concentrate on getting the best possible deal from the 27 EU states for Scotland and the UK.

“The way to do that is for everyone - Brexiteers and Remainers - to rally round the PM’s plan, which delivers a pragmatic Brexit, and was signed off by the whole Cabinet at Chequers,” said the Scottish Secretary.

His Cabinet colleague Michael Gove, said to have delivered a key intervention during the Chequers summit in favour of the May compromise, rejected what he called “fake outrage” and insisted what was on offer was “a proper Brexit”.

The Environment Secretary, who was a leading light in the Leave campaign, accepted Friday’s agreement was not everything the Brexiteers had wanted but stressed it was a “perfect balance” between sharing regulations with the EU on 20 per cent of the UK economy - a “common market of goods” - but being outside the bloc’s remit on 80 per cent of it ie on services.

The Scot said: “Those of us who believe we want to execute a proper Brexit, and one that is the best deal for Britain, have an opportunity now to get behind the Prime Minister in order to negotiate that deal."

He rejected a view attributed to Mr Johnson, that selling the compromise plan was like “polishing a turd,” stressing from here “collective responsibility reigns”.

But Mr Davis’s move will now embolden some Conservative MPs, alarmed and angered by the soft nature of Mrs May’s Brexit plan, to add their signatures to letters calling for a leadership contest – 48 are needed.

Yet some Brexiteers are already resigned to any challenge failing.

One said: “There could well be enough letters sent to Sir Graham Brady[Chairman of the backbench 1922 Committee] to set in motion a confidence vote in Mrs May’s leadership. But, in any case, the PM will win hands-down.”

Another backbencher said: “Only those blinded by their own ideology will challenge the PM, which is unfortunately a few too many of my colleagues. But if they trigger the confidence vote, May will win it very easily.”

Andrew Bridgen, the Leicestershire Tory, expressed his “deep disappointment” at the Chequers plan, saying he would not back it "if the EU were paying us". But he stopped short of calling for a confidence vote in his party leader, saying: "We're not there yet."

Veteran Eurosceptic Sir Bill Cash said there was a “lot of unhappiness” about Mrs May’s compromise proposal but he stressed he wanted to see the details of it when the White Paper is published on Thursday.

"Is this going to be a proper Brexit? There will be a massive discussion about all this," stressed the Staffordshire MP.

But Andrew Bowie, the MP for West Aberdeenshire and Kincardine, explained that he was “very happy” with what he described as a “pragmatic and sensible Brexit proposal that is good for business and jobs”.

He added:  It's time for all the party, and indeed the whole country, to rally behind the PM and ensure a united front as we enter the final phase of the negotiations.”

Today, more Tory MPs will be given a private Downing St briefing on the PM’s compromise proposal before attending a meeting this evening of the 1922 Committee in the House of Commons when Mrs May will face a showdown with some of her Brexiteer critics.

Before that, she will deliver a Commons statement when she will defend her Chequers Plan.  

The PM will say: “In the two years since the referendum result we have had a spirited national debate with robust views echoing round the Cabinet table as they have on breakfast tables up and down our country.

“Over that time, I have listened to every possible idea and every possible version of Brexit. This is the right Brexit,” she will declare.

Mrs May will tell MPs it offers, among other things: a complete end to freedom of movement; an end to the jurisdiction of the European Court in the UK; a Brexit dividend to spend on domestic priorities like the NHS; frictionless trade in goods and flexibility on services; no hard Irish border; departure from the Common Agriculture and Fisheries Policies; a parliamentary lock on all new EU rules and regulations and freedom to strike new trade deals around the world.

Mrs May will add: “This is the Brexit that is in our national interest. It is the Brexit that will deliver on the democratic decision of the British people.”

However, the dramatic resignation of Mr Davis has cast major doubt about the survival of the PM’s Brexit plan and indeed about her own political future.

Mr Davis told BBC Radio 4's Today: "When we debated this at Cabinet on Friday my opening remark to Theresa was 'Prime Minister, as you know I'm going to be the odd-man-out in this'. She knew this because I had written to her earlier in the week.

"Cabinet collective responsibility applied so I didn't say anything thereafter. That was because I was thinking about the consequences.

"I took the view at the time this was not the best strategy, that there were better strategies available - we have been establishing them.

"I thought it would be a risk at least of delivering a poor outcome. I was very clear on Friday and I took two days to think through some, for me, very important decisions."

The outgoing Brexit Secretary said "we are giving too much away, too easily" in the exit talks and warned that is a "dangerous strategy".

Mr Davis said other Cabinet members had asked for changes to be made to the Brexit policy on Friday, but none had been made.

He admitted he had "lost the argument in Cabinet", adding: "In my view, this policy has got a number of weaknesses.

"I would be front and centre in delivering this policy, explaining it to the House, persuading the House it is right, and then going out and delivering it with the EU.

"Frankly, just as it was known what the policy was, it was also known I had concerns about it.

"It would not have been a plausible thing to do and I wouldn't have done a good job at it."

Mr Davis denied weakening the Prime Minister, saying: "It is one day, she has got to have a Brexit Secretary who will deliver on her strategy.

"That is not weakening, that is actually enhancing the effectiveness of the strategy."

He said he wanted to speak to Mrs May "face to face" on Sunday night but had spoken to her by telephone as she was at her home in Sonning, Berkshire.

He added: "I like Theresa May, I think she is a good PM. We have a difference over this strategy."

Mr Davis said he would continue to argue for the UK being "as firm as possible" with the European Union.

He said: "It seems to me we are giving too much away too easily and that's a dangerous strategy at this time.

"Hopefully we will resist very strongly any attempt to get any further concessions from us on this, because I think this further than we should have gone already."

Mr Davis said he had made a "decision of principle" and said "no" when asked if he wanted others to follow him out the Government.

He said: "It is not for me to make other people's decisions.

"These decisions are very, very hard to make. They have consequences, career-ending consequences, all of that.

"The simple truth is people can only make these decision of conscience, decisions of principle, by themselves, in their own minds.

"You can't make the decision for somebody else. You can't offload it onto somebody else."