BORIS Johnson has quit as Foreign Secretary, prompting speculation that he could be about to challenge Theresa May for the leadership of the Conservative Party.

Johnson's resignation came hours after the departure of Brexit Secretary David Davis.

There had been growing speculation about Johnson after he failed to attend a meeting of the Government's Cobra emergencies committee as well as a summit of Western Balkan nations being held in London.

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His security team included six police motorcade riders, along with a Land Rover and his official car and were left waiting on his driveway for most of the day.

Officers twice warned journalists the Foreign Secretary was about to leave, only to then say they had been told to stand by.

At 3pm, a statement was issued by Downing Street to say: "This afternoon, the Prime Minister accepted the resignation of Boris Johnson as Foreign Secretary.

"His replacement will be announced shortly. The Prime Minister thanks Boris for his work."

It later emerged that Johnson had been "spiked", meaning his resignation was announced by Downing Street before the now former Foreign Secretary had finished his resignation letter.

Scottish Tory leader Ruth Davidson said: "The Prime Minister is correct to accept the Foreign Secretary's resignation.”

The SNP Westminster leader Ian Blackford said: “The Foreign Secretary should never have had the opportunity to resign. He should have been sacked months ago as a national embarrassment.”

EU council president Donald Tusk tweeted: “Politicians come and go. The problems they have created remain. The mess of Brexit is the biggest problem in the history of EU-UK relations.”