Boris Johnson has resigned as foreign secretary, warning that the dream of Brexit was "dying, suffocated by needless self-doubt".

Johnson's dramatic decision on Monday came just hours after David Davis quit as Brexit secretary, saying the UK was giving away “too much, too easily” to the European Union.

In an astonishing day at Westminster that has left the Conservative party reeling and the government's Brexit strategy in doubt:

-- Johnson will be replaced as foreign secretary by Jeremy Hunt, who has been health secretary for the last six years.

-- Matt Hancock, the culture secretary, was promoted to the health secretary job to replace Hunt.

-- The double departure of the two most prominent Brexiteers in cabinet amounts to the most treacherous moment in Theresa May’s premiership. But she vowed to stay on and fight any potential leadership challenge.

In a letter to the PM, Johnson said Britain appeared to be "heading for a semi-Brexit", with much of the economy still locked in the EU system but with no UK control over that system.

He said it was wrong to accept "huge amounts" of EU law without being able to influence those laws being made. "In that respect we are truly headed for the state of colony," he claimed.

"Brexit should be about opportunity and hope," he added. "It should be a a chance to do things differently, to be more nimble and dynamic, and to maximise the particular advantages of the UK as an open, outward-looking global economy.

"That dream is dying, suffocated by needless self-doubt."

In response, the PM said she was "sorry – and a little surprised" that he had decided to resign following their "productive discussions" at Chequers.

She wrote: "During the EU referendum campaign, collective responsibility on EU policy was temporarily suspended. As we developed our policy on Brexit, I have allowed cabinet colleagues considerable latitude to express their views.

"But the agreement we reached on Friday marks the point where that is no longer the case, and if you are not able to provide the support we need to secure this deal in the interests of the United Kingdom, it is right that you should step down."