Brexit is on course for a lengthy delay after MPs rejected Theresa May's EU Withdrawal Agreement by a margin of 58 votes.
In dramatic scenes in the House of Commons, MPs voted by 344 to 286 against the deal as hundreds of protesters staged a noisy demonstration outside on the day when the UK was due to leave the European Union.
The result of the crunch vote means that the UK has missed an EU deadline to secure an extension of the Brexit process and leave with a deal on May 22.
Mrs May now has until April 12 to go back to Brussels with new proposals and seek a longer extension to the negotiation process, or see the UK leave without a deal that day.
She said: "I think it should be a matter of profound regret to every member of this House that once again we have been unable to support leaving the European Union in an orderly fashion.
"The implications of the House's decision are grave.
"The legal default now is that the United Kingdom is due to leave the European Union on 12 April, in just 14 days' time.
"This is not enough time to agree, legislate for and ratify a deal, and yet the House has been clear it will not permit leaving without a deal.
"And so we will have to agree an alternative way forward."