British prime minister Theresa May is to travel to Europe to seek concessions on her Brexit deal, after calling off a crunch House of Commons vote in which she was expected to go down to a heavy defeat.
In a statement to MPs, Mrs May also said the government was stepping up preparations for a possible no-deal Brexit.
And she said that MPs who were threatening to vote against the deal she secured with Brussels must ask themselves the fundamental question: "Does this House want to deliver Brexit?"
If the answer was yes, she said that they needed to consider whether they were prepared to make "compromises" in order to make good on the 2016 referendum vote to leave the EU.
Announcing the decision to delay the vote on the Brexit deal, Mrs May told the Commons that if it had gone ahead as planned, the Government would have been defeated by a significant margin.
"I have listened very carefully to what has been said in this chamber and out of it by members from all sides," she said.
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"From listening to those views it is clear that while there is broad support for key aspects of the deal, on one issue, the Northern Ireland backstop, there remains widespread and deep concern.
"As a result, if we went ahead tomorrow it would be rejected by a significant margin."
Mrs May's statement came amid dramatic scenes at Westminster, as news of her plan to postpone Tuesday's "meaningful vote" broke just minutes after Downing Street had insisted it was going ahead.
It is understood that the PM had been warned that she faced a large-scale defeat when MPs voted at the end of five days of debate in the Commons on her plans.
She spoke with her Cabinet colleagues by a telephone conference call before addressing the Commons.
Mrs May said that as long as Parliament failed to agree a deal, the risk of an "accidental no-deal" would increase, and so the Government was stepping up its no-deal planning.
"Even though I voted Remain, from the moment I took up the responsibility of being Prime Minister of this great country I have known that my duty is to honour the result of that (referendum) vote," she said.
"I am determined to do all I can to secure the reassurances this House requires to get this deal over the line and deliver for the British people."
Mrs May said: "Many of the most controversial aspects of this deal - including the backstop - are simply inescapable facts of having a negotiated Brexit.
"Those members who continue to disagree, need to shoulder the responsibility of advocating an alternative solution that can be delivered."
The PM added: "So, if you want a second referendum to overturn the result of the first, be honest that this risks dividing the country again, when as a House we should be striving to bring it back together.
"If you want to remain part of the single market and the customs union, be open that this would require free movement, rule-taking across the economy, and ongoing financial contributions - none of which are in my view compatible with the result of the referendum.
"If you want to leave without a deal, be upfront that in the short term, this would cause significant economic damage to parts of our country who can least afford to bear the burden.
"I do not believe that any of those courses of action command a majority in this House."
