The British Prime Minister's Brexit strategy has been dealt a devastating blow after the House of Commons rejected her EU Withdrawal Agreement by an overwhelming majority for the second time.
MPs voted by 391 to 242 against the deal, despite Theresa May's assurance that new agreements reached with Jean-Claude Juncker in Strasbourg last night would ensure the UK cannot be trapped in the controversial backstop arrangement indefinitely.
Although the 149 margin was reduced from the record 230-vote defeat of the first "meaningful vote" in January, Mrs May was left far adrift from a majority with just 17 days to go to the scheduled date of Brexit on 29 March.
European Commission president Mr Juncker had already warned that if MPs turned down the package agreed in Strasbourg yesterday, there would be "no third chance" to renegotiate.
In line with a promise set out by Mrs May last month, MPs are now due to vote tomorrow on whether they are willing for the UK to leave the EU without a deal on 29 March.
If they reject no-deal as most Westminster observers expect, a third vote will follow - probably on Thursday - on authorising Mrs May to request an extension of the two-year Article 50 negotiation process.
An extension requires the unanimous agreement of all 27 remaining member states, and Mr Juncker has warned that it cannot stretch beyond 23 May unless the UK takes part in the European Parliament elections starting on that date.
Speaking after tonight's vote, Mrs May said that the choices facing the UK were "unenviable", but because of
the rejection of her deal, "they are choices that must be faced".
She said she "profoundly regrets the decision this House has taken tonight".
The Prime Minister said: "I continue to believe that by far the best outcome is the UK leaves the European Union in orderly fashion with a deal.
"And that the deal we have negotiated is the best and indeed only deal available."
Announcing the free vote, Mrs May told MPs: "This is an issue of grave importance for the future of our country.
"Just like the referendum there are strongly held and equally legitimate views on both sides.
"For that reason, I can confirm that this will be a free vote on this side of the House."
The Prime Minister said she had "personally struggled with this choice" but the best way to leave was "in an orderly way" with a deal.
Mrs May stressed her responsibilities for Northern Ireland, where Stormont is still suspended.
She said: "I'm conscious of my duties as Prime Minister of Great Britain and Northern Ireland and the potential damage to the union that leaving without a deal could do, when one part of our country is without a devolved government."
Labour leader Jeremy Corbyn said: "The Government has been defeated again by an enormous majority.
"They must now accept their deal is clearly dead and does not have the support of this House.
"Quite clearly, no-deal must be taken off the table."
Mr Corbyn said the Commons has to come together with a proposal that could be negotiated, adding Labour will put forward its plans again.
He suggested a general election should also be held.
On Twitter the EU's chief Brexit negotiator Michel Barnier said the impasse over the UK's withdrawal from the EU could only be solved in the UK.
A spokesman for European Council president Donald Tusk said: "We regret the outcome of tonight's vote and are disappointed that the UK Government has been unable to ensure a majority for the Withdrawal Agreement agreed by both parties in November.
"On the EU side we have done all that is possible to reach an agreement. Given the additional assurances provided by the EU in December, January and yesterday, it is difficult to see what more we can do.
"Should there be a UK reasoned request for an extension, the EU27 will consider it and decide by unanimity.
"The EU27 will expect a credible justification for a possible extension and its duration. The smooth functioning of the EU institutions will need to be ensured."
However, Brexiteer Jacob Rees-Mogg has warned those looking to delay Brexit that it would not be easy to extend Article 50.
"The default legal position remains, as the Prime Minister pointed out, that we still leave on March 29," he told the BBC.
"It would have to be changed by law, and the law is not easy to change."
He added: "The only way of changing the date is for an extension granted by the EU ... what purpose would this extension serve? What is going to be asked for in this extension?"
"Today is the day. Let's get this done."
Earlier, the Cabinet gave its approval to Mrs May's package at an early-morning meeting in 10 Downing Street which ended with the PM telling colleagues: "Today is the day. Let's get this done."
But the momentum moved sharply against the Prime Minister shortly afterwards, as Attorney General Geoffrey Cox released formal legal advice that the changes secured by Mrs May "reduce the risk" that the backstop will be permanent, but do not remove it altogether.
The Star Chamber of lawyers convened by the Brexit-backing European Research Group declared that three new documents agreed in Strasbourg failed to deliver the legally-binding changes demanded by the Commons.
And the Democratic Unionist Party - which props up Mrs May's minority administration in the Commons - said its ten MPs would vote against the latest deal as "sufficient progress has not been achieved at this time".
The Prime Minister warned MPs that "Brexit could be lost" if they gave her deal the thumbs-down again.
But she met a wall of hostility from opposition parties, while only a handful of the 118 Tories who rebelled in January said they would switch sides to back her.
Shadow Brexit secretary Sir Keir Starmer said that "no significant changes" had been secured in two months of negotiations and the Government's strategy was "in tatters".
Brexit figurehead and former foreign secretary Boris Johnson told the Commons that Mrs May and Mr Cox had "sowed an apron of fig leaves that does nothing to conceal the embarrassment and indignity of the UK".
Charles Walker, vice chairman of the 1922 Committee of backbench Tory MPs, warned that defeat in the second "meaningful vote" on Tuesday evening would lead to a general election.