The EU has ruled out reworking the Brexit deal it agreed to two weeks ago and will prepare for a no-deal scenario, as the British PM postpones the vote on leaving the UN.
British Prime Minister Theresa May has postponed a parliamentary vote on her Brexit deal to avoid a crushing defeat, saying she would return to the EU for further talks in a perceived sign of weakness that sent the pound plunging.
In an emergency statement to the House of Commons, May conceded the agreement she struck with the EU last month faced defeat by a "significant margin" of MPs on Tuesday.
She said she had "no doubt this deal is the right one" but promised to seek "additional reassurance" from the EU over a controversial provision on Northern Ireland.
The president of the European Council called a meeting of EU leaders to discuss Brexit, but warned they would not renegotiate the withdrawal deal.
"We will not renegotiate the deal, including the backstop, but we are ready to discuss how to facilitate UK ratification," he wrote.
"As time is running out, we will also discuss our preparedness for a no-deal scenario."
A spokesman for Tusk said the timing of the meeting, which will come on the first day of a planned European Council summit, was still to be determined.
"Based on Prime Minister May's decision to defer the vote, President Tusk has decided to call European Council, Article 50, on Thursday," he said.
"There will be no renegotiation of the November 25 agreement but the EU27 stands ready to discuss how to facilitate UK ratification," the spokesman said.
"We are in contact with the UK on how it wants to proceed," he said, adding that Tusk is consulting the other 27 leaders of the remaining EU member states.
The news sent the pound plunging. At about 1600 GMT, sterling sank by more than 1.5 percent to $1.2527, the lowest level since April 2017.
"This is yet another blow for companies desperate for clarity," said Carolyn Fairbairn, head of the Confederation of British Industry big business lobby.
May conceded that her move increased the uncertainty over the terms of Britain's withdrawal from the EU after four decades in March next year.
"For as long as we fail to agree a deal, the risk of an accidental no deal increases," she told MPs.
"So the government will step up its work in preparation for that potential outcome."
'Govern or quit'
May faced a huge rebellion of her own Conservative MPs over the deal, primarily over a "backstop" clause designed to keep open Britain's border with Ireland.
"I still believe there is a majority to be won in this House in support of it if I can secure additional reassurance on the question of the backstop," she told MPs.
After speaking with EU leaders including EU President Donald Tusk and German Chancellor Angela Merkel at the weekend, she said she would continue talks ahead of a Brussels summit on Thursday and Friday.
However, she warned rebel MPs that their demands to remove the clause entirely were unrealistic, saying: "There is no deal available that does not include the backstop."
But as opposition MPs shouted "resign" at May, Labour leader Jeremy Corbyn said: "The government has lost control of events and is in complete disarray."
He questioned what she could achieve by going back to the EU leaders.
"This is a bad deal for Britain, a bad deal for our economy and a bad deal for our democracy," he said.
"Our country deserves better than this."
Labour had previously indicated it could table a confidence motion in May if she lost the vote on Tuesday, and there were calls from some MPs for it to act after Monday's U-turn.
The Scottish National Party (SNP) said it would back a vote of no confidence, with its Scottish First Minister Nicola Sturgeon, tweeting: "This shambles can't go on."
May had risked a leadership challenge from within her party if she lost, with eurosceptics arguing her Brexit deal would leave Britain tied for years to the EU rules.
Critics said delaying the vote also highlighted her weakness.
"This is not governing, it risks putting Jeremy Corbyn into government by failing to deliver Brexit," said leading Conservative rebel Jacob Rees-Mogg, who led a foiled attempt to unseat May last month.
"We cannot continue like this. The prime minister must either govern or quit."
Eurosceptics in May's Conservative party and the Northern Irish party that props up her government hate the provision in the Brexit deal designed to keep open the border with Ireland -- the so-called backstop.
It would kick in after a post-Brexit transition if no new trade deal were agreed between London and Brussels, and could see Britain caught for many years in a customs union with the EU.
Conservatives such as former foreign minister Boris Johnson, a leading Brexiteer, want May to renegotiate a unilateral exit from the backstop.
But, speaking in Dublin, Irish Prime Minister Leo Varadkar said the current deal "is the only agreement on the table.
"It took over a year and a half to negotiate, it has the support of 28 governments, and it's not possible to re-open any aspect of that agreement without re-opening all aspects of it," he said.
Some EU officials have however mentioned the possibility of changes to the accompanying political declaration on future trade ties between Britain and the EU after Brexit.
Some MPs are pressing for a second referendum on Brexit. They were given hope on Monday by a ruling from the European Court that Britain was free to halt withdrawal from the bloc unilaterally.