Theresa May will make a direct plea to EU leaders later asking to postpone Brexit for three months, hours after telling the British public a delay was “a matter of great personal regret”.
At an EU summit in Brussels, she will try to persuade the other 27 countries to delay the UK’s exit beyond 29 March.
On Wednesday, the PM made a speech blaming the delay on MPs and telling the nation she was “on their side”.
Meanwhile, Jeremy Corbyn is also due in Brussels for separate Brexit talks.
EU leaders are expected to arrive at the two-day summit from 13:00 GMT.
The BBC’s Europe correspondent Kevin Connolly said the EU side “appears to hold all the aces” at the summit, with some countries including France “sceptical of the value of making an offer” of an extension.
Speaking in the German Parliament, Angela Merkel said the EU could meet Mrs May’s request to delay Brexit if in the next week there was a “positive vote” on the withdrawal agreement in the UK Parliament.
The German Chancellor said European elections at the end of May would have to be considered during discussions on the suggested extension deadline of 30 June, adding: “But of course we can certainly talk about a short term extension.”
The UK is set to leave the EU next Friday unless the law is changed. The current default position for leaving is without a withdrawal agreement.
Mrs May agreed a deal with the EU, but MPs have rejected it twice.
She has asked the EU for a short extension of the two-year Brexit process until 30 June, but any extension needs to be agreed to by all EU members.
European Council President Donald Tusk said he believed the EU would agree to a short extension, but this would only be if Mrs May’s deal is signed off by MPs next week. Another EU summit next week could be called in an emergency if needed, he said.
Mr Tusk said the “question remains open” as to how long a delay the other EU leaders would support.
Leaders want to avoid no-deal Brexit
Beware the reports of “huge” differences between EU leaders when it comes to a Brexit delay and the way forward in the coming days.
Take Germany’s Angela Merkel and France’s Emmanuel Macon: There are big differences in their political styles.
And big differences in the message they want to send their own domestic audiences (tough for France; open for Germany) when talking about Brexit.
But like most EU leaders – irritation, frustration and Brexit fatigue aside – they would rather avoid a costly no-deal Brexit.
Chancellor Merkel, like European Council President Donald Tusk has announced she will work “until the last hours” to try to avoid it.
And while EU leaders have ruled out re-opening the Brexit withdrawal agreement and the “backstop” text, you can bet they’ll discuss a longer Brexit delay at their summit today.
They will also discuss the short delay requested by Theresa May, in case – as the EU fears – chaos and division continue next week in Westminster.
In her speech from Number 10 on Wednesday evening, Mrs May insisted she would not be willing to postpone Brexit any further than 30 June, despite appeals from some MPs.
She added: “Of this I am absolutely sure. You, the public, have had enough.
“You are tired of the infighting, tired of the political games and the arcane procedural rows, tired of MPs talking about nothing else but Brexit when you have real concerns about our children’s schools, our National Health Service, knife crime.
“You want this stage of the Brexit process to be over and done with. I agree. I am on your side.”
She said it was now up to MPs to decide whether they wanted to leave with her deal, no deal or not to leave at all. But she warned that the latter option could cause “irreparable damage to public trust” in politicians.
Foreign Secretary Jeremy Hunt said the UK would be faced with three options if Mrs May’s deal was defeated again next week: revoke Article 50; leave without a deal; or a longer extension could be granted at an emergency EU summit, but with “onerous conditions”.
“The choice that we have now is one of resolving this issue or extreme unpredictability,” Mr Hunt told BBC Radio 4’s Today programme.
He also defended the prime minister’s statement, saying Mrs May was under “extraordinary pressure” and MPs have a “special responsibility” in a hung Parliament.
Labour leader Jeremy Corbyn is also heading to Brussels, where he will meet the EU’s chief Brexit negotiator, Michel Barnier, and the leaders of seven European countries to discuss alternatives to Mrs May’s Brexit plan.
He said Mrs May was “in complete denial about the scale of the crisis” facing the country and was “unable to offer the leadership the country needs”.
Her speech also sparked an angry response from MPs across the House of Commons, with some calling her comments “toxic” and “reckless”.
There was a strong reaction to Mrs May’s speech on Wednesday evening.
Labour’s Lisa Nandy described Mrs May’s statement as “disgraceful” for “pitting Parliament against the people”, while fellow Labour MP Wes Streeting added it was “incendiary and irresponsible” at a time when some MPs had received death threats.
Pro-EU Tory Sam Gyimah, who quit as a minister over her deal, described her remarks as “toxic” and said the “blame game” was “a low blow”.