David Davis 'felt he had no choice but resignation'

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Image caption David Davis' unhappiness has been not secret for some time

After many months of rumours that he would pull the plug, David Davis has actually quit as Brexit Secretary.

His unhappiness in government has been no secret for some time, but after the prime minister's Chequers agreement with cabinet ministers to pursue closer ties with the EU than he desired, he found his position untenable.

After a visit to Downing Street on Sunday he concluded that he had no choice but to walk. Junior ministerial colleague Steve Baker has also quit alongside him from the Brexit department. David Davis' move, while not completely surprising, throws doubt on to how secure the government's Brexit strategy is.

Some of Theresa May's colleagues had urged her to face down her Brexiteer ministers but Number 10 had hoped to keep them all on side, and a carefully designed strategy to move them to her position brokered an agreement in cabinet at the end of their day-long meeting at Chequers on Friday .

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Image caption Theresa May secured her cabinet's support at a meeting at Chequers on Friday

But Mr Davis, who was meant to be responsible for Brexit policy, felt, according to colleagues, that he was "wondering if he really had a proper job" after Number 10 chose to follow a very different path to the now former Brexit secretary's intention.

Mr Davis has been frustrated for some time after the most senior official at the Department for Exiting the EU - Olly Robbins - was moved into Number 10 to work directly for Theresa May.

To some former Remainers, Mr Davis' departure could even be considered a temporary relief. One of his fellow ministers remarked, "it's just a personal outburst", adding: "He is not exactly the cleverest, he has always struggled to muscle into any of the complicated arguments."

But conditions in the Tory party are febrile. Theresa May had carefully constructed her cabinet with a balance of Brexiteers and former Remainers. With no majority, and unhappiness on the back benches, it adds instability at a time when the prime minister was pursuing calm.

And when she was hoping to project an image to Brussels of authority and stability, it is a headache she could well do without. He could provide a rallying point from outside government for those forces in the Tory party who believe the Brexit plan the prime minister is pursuing is not the Brexit that a clear but narrow majority of the public chose.

Image caption Michael Gove was tipped as a replacement for David Davis

Westminster being Westminster, eyes will immediately turn to who will replace him. The most likely candidate it seems at this stage is Michael Gove who has pitched himself as the Brexiteer that "remainers can do business with".

His public appearances defending the Brexit policy over the weekend make him certainly near the top of the list for one of the most important jobs in government.