Update 6.57pm: Boris Johnson has dramatically quit as foreign secretary, complaining that Theresa May’s plan for Brexit would leave the UK a “colony” of the European Union.
In a scathing resignation letter to the Prime Minister, Mr Johnson said that, under her leadership, the UK was “heading for a semi-Brexit”, with the dream of an outward-looking global Britain “dying, suffocated by needless self-doubt”.
Mr Johnson shock departure was the second resignation of a Cabinet “big beast” in less than 24 hours, after Brexit secretary David Davis walked out late on Sunday.
Brexit minister Steve Baker also left the Government.
Both Mr Johnson and Mr Davis had signed up on Friday to Mrs May’s blueprint for Brexit at an all-day summit at Chequers which the Prime Minister believed had secured Cabinet unity behind her proposals.
But her administration was thrown into disarray within 48 hours, as first Mr Davis and then Mr Johnson said that they could not commit themselves to promote the plans under the doctrine of collective responsibility.
Mr Johnson wrote: “On Friday, I acknowledged that my side of the argument were too few to prevail and congratulated you on at least reaching a Cabinet decision on the way forward.
“As I said then, the Government now has a song to sing.
“The trouble is that I have practised the words over the weekend and I find they stick in the throat.
“We must have collective responsibility.
“Since I cannot in all conscience champion these proposals, I have sadly concluded that I must go.”
- Press Association
By Juno McEnroe, Political Correspondent
British foreign secretary Boris Johnson has resigned from Theresa May's Cabinet, a move which is now likely to trigger a leadership challenge against the British prime minister.
Irish ministers today have declined to comment on the resignation crisis now engulfing 10 Downing Street and how this might affect Brexit.
Mr Johnson's move comes after the resignation of Brexit secretary David Davis, whose shock decision to quit overnight has thrown Ms May's hoes a new alternative Brexit proposal into chaos.
The UK prime minister is expected to meet her Tory backbenchers this evening and is also scheduled to address the House of Commons shortly.
But Mr Johnson's move now makes Ms May's position even more fragile.
The foreign secretary had criticised her new Brexit plan at Chequers last week. In a crude outburst, the outspoken Tory told the meeting of the British Cabinet that defending the plans was like “polishing a turd”.
Mr Johnson today had been scheduled to host a launch at the EU-Western Balkans summit in London today but pulled out.
His resignation now increases the chances of a leadership challenge against the British prime minister, a scenario that could also trigger potentially fresh elections in Britain.
The dramatic developments come as Britain was set to launch a white paper this week setting out future relations with the European Union after Brexit.
It is less than nine months to Brexit. Furthermore, London has until just October to finalise a deal with the EU and Ireland about its divorce from the union.