British MPs have voted down Prime Minister Theresa May's Brexit divorce deal by a crushing margin, triggering political upheaval that could lead to a disorderly exit from the European Union or even to a reversal of the 2016 decision to leave.

MPs voted 432 to 202 to defeat the proposal, the worst parliamentary defeat for a government in recent British history.

Mrs May had called for politicians to back her deal or risk "letting the British people down".

But an unprecedented 118 of her own Conservative MPs — both Brexiteers and supporters of EU membership — joined forces to vote down the deal.