Prime Minister Theresa May asked the EU on Wednesday to delay Brexit until June 30, as she scrambled to contain a deepening political crisis, but faced warnings that Britain could still crash out of the bloc in nine days.
The pound plunged on currency markets as European Union leaders and British parliamentarians responded with scepticism to her request, made ahead of a Brussels leaders' summit on Thursday.
Exactly 1,000 days on from Britain's seismic 2016 referendum vote to leave the EU, a divorce deal negotiated by May is blocked in Parliament and uncertainty grips the country.
She is seeking to put back the March 29 exit date to try one more time to get her agreement passed, but said any further postponement would undermine voters' trust.
However, the European Commission advised EU leaders that a shorter delay to May 23 or a much longer one until at least the end of 2019 would be preferable.
The other 27 EU leaders must unanimously agree any delay, but Commission President Jean-Claude Juncker said it was unlikely they would take a decision this week unless London set out a clear plan, suggesting another meeting might be needed next week.
A spokesman for German Chancellor Angela Merkel welcomed London's "clear request", and said she would "make every effort" to bring about an agreement at the Brussels summit.
But her foreign minister Heiko Maas of the junior coalition partner Social Democrats was less conciliatory, saying May's letter "only pushes the solution further down the road".
In Paris, French Foreign Minister Jean-Yves Le Drian also had a tough message.
"A situation in which Mrs May is unable to deliver sufficient guarantees on the credibility of her strategy at the European Council meeting would lead to the request being refused and a preference for a no deal," he told Parliament.
May reluctantly accepted this week that a delay to Brexit is now needed, and told MPs Wednesday that she had written to EU President Donald Tusk "informing him that the UK seeks an extension... to June 30".
But she was confronted with a barrage of criticism from Brexit hardliners who want to leave on March 29 regardless, as well as pro-EU lawmakers who want a longer delay to seek a new strategy.
May faced shouts of "resign", while opposition Labour leader Jeremy Corbyn accused her of leading Britain into "crisis, chaos and division".
Speaker of the House of Commons John Bercow later granted Labour's request for an emergency debate on the delay.
In her letter to Tusk – addressed as "Dear Donald" – May said she intended to bring her deal back to the Commons "as soon as possible," arguing that if it passed, she would need the delay until June 30 to implement the treaty.