Theresa May says she has called off Tuesday’s crucial vote on her Brexit deal because it “would be rejected by a significant margin”.
She said MPs backed much of the deal she has struck with the EU but there was concern over the Northern Irish backstop.
She said she believed she could still get the deal through if she addressed MPs’ concerns.
And that, she added, was what she intended to do in the next few days.
However, Speaker John Bercow – who chairs debates in the House of Commons – called on the government to give MPs a vote on whether Tuesday’s vote should be cancelled, saying it was the “right and obvious” thing to do given how angry some MPs were about the cancellation.
In her statement Mrs May said she would be “deferring” the Commons vote until she had made efforts to address concerns over the Northern Ireland border “backstop” plan.
She has not so far indicated when the Commons vote on her deal will be held – but she did note that it would have to happen before 21 January.
Mrs May told MPs she would be speaking to EU leaders ahead of a summit later this week, about the “clear concerns” expressed by MPs.
And she would also be “looking closely at new ways of empowering the House of Commons to ensure that any provision for a backstop has democratic legitimacy”.
She wants to enable MPs to place obligations on the government “to ensure that the backstop cannot be in place indefinitely”.
She again rejected all other alternatives that have been proposed to her deal – including a further referendum and leaving without a deal.
She said her deal “gives us control of our borders, our money and our laws – it protects jobs, security and our Union”.
“It is the right deal for Britain. 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,” she added.
Asked by Lib Dem leader Sir Vince Cable if EU leaders had indicated they were ready to ditch the backstop, she said: “A number of European leaders I’ve spoken to have indicated that they are open to discussions to find a way to provide reassurance to members of this House on that point.”
Labour leader Jeremy Corbyn said the prime minister had “lost control of events” and the government was in “complete chaos” – and urged her to stand down.
Mr Corbyn faced a call from Sir Vince Cable, who is campaigning for a further referendum, to table a vote of no confidence in the prime minister, which he said his party would back.
SNP leader and Scotland’s First Minister Nicola Sturgeon earlier tweeted to Jeremy Corbyn: “If Labour, as official opposition, lodges motion of no confidence in this incompetent government tomorrow, @theSNP will support & we can then work together to give people the chance to stop Brexit in another vote. This shambles can’t go on – so how about it?”
Leading Conservative Brexiteer Jacob Rees-Mogg said in a statement that Mrs May lacked the “gumption” to put her “undeliverable” deal before MPs.
“This is not governing, it risks putting Jeremy Corbyn into government by failing to deliver Brexit. We cannot continue like this. The prime minister must either govern or quit.”
Mr Rees-Mogg is trying to get enough Tory MPs to submit letters of no confidence in the PM to trigger a leadership contest.
The pound fell sharply in response to the reports earlier of a likely delay to the Commosn vote, shedding 0.5% versus the US dollar to stand at $1.26, an 18-month low. The pound was 0.8% down against the euro.
Mrs May’s Commons statement will be followed by a statement from Commons leader Andrea Leadsom – and then a statement from the Brexit secretary Stephen Barclay on Article 50 – the legal mechanism taking the UK out of the EU on 29 March.
The deputy leader of the DUP – the Northern Ireland party whose backing Theresa May needs to win key votes – Nigel Dodds, said the situation was “quite frankly a bit of a shambles” and the PM was paying the price for crossing her “red lines” when it came to Northern Ireland.
He told Mrs May: “Come back with the changes to the withdrawal agreement or it will be voted down.”
DUP leader Arlene Foster said she had told the prime minister in a phone call that the “backstop must go”.
Theresa May’s deal has been agreed with the EU – but it needs to be backed by the UK Parliament if it is to become law ahead of the UK’s departure.
Mrs May has also been speaking to EU leaders about re-opening the withdrawal agreement, something both sides have previously ruled out.
It comes as the European Court of Justice ruled the UK could cancel Brexit without the permission of the other 27 EU members.
But European Commission spokeswoman Mina Andreeva said the EU would not renegotiate the Withdrawal Agreement.
“As President Juncker said, this deal is the best and only deal possible,” she said.
“We will not renegotiate – our position has therefore not changed and as far as we are concerned the United Kingdom is leaving the European Union on 29 March, 2019.”
The BBC’s Brussels reporter Adam Fleming said Mrs May was “trying get more legal oomph behind the language” in the withdrawal agreement about the EU using “best endeavours” to get a trade deal which would remove the need for the backstop to be used.
Dozens of Conservative MPs had been planning to join forces with Labour, the SNP, the Lib Dems, Plaid Cymru and the DUP to vote down Mrs May’s deal.
The Tory rebels and the DUP do not like the Northern Ireland “backstop”, a legally-binding proposal for a customs arrangement with the EU, which would come into force if the two sides’ cannot agree a future relationship which avoids the return of a visible Northern Ireland border.
Tory MPs say it is unacceptable because it would result in new regulatory barriers between Northern Ireland and the rest of the UK and could continue indefinitely, because the UK would not be able to leave without the EU’s approval.