Britain and the EU made headway in eleventh-hour talks on Tuesday to reach a Brexit deal in time for a leaders' summit, but with hours left to clinch an agreement it was still unclear if London could avoid delaying its scheduled October 31 departure.
The European Union's Brexit negotiator Michel Barnier made clear at a meeting of ministers in Luxembourg that if an agreement wasn't reached on Tuesday, it would be too late to send anything for the bloc's leaders to approve at their meeting on Thursday and Friday.
However, as technical talks continued in Brussels, word emerged that gaps on an agreement had narrowed and the two sides were close to agreeing on a text.
One EU official said an agreement was "close but not 100% certain", adding "there are still parts that need to be nailed down". Others were more cautious: one senior official said it was "way too premature" to conclude that a deal was at hand.
Sterling surged to its highest level against the dollar
and the euro since May on rising hopes for a deal.
The main sticking point in talks has been the border between EU member Ireland and the British province of Northern Ireland.
Three years after Britons voted in a referendum to quit the EU, negotiators are still wrestling with the question of how to
prevent the border becoming a backdoor into the bloc's single market without erecting controls which could undermine the 1998 peace agreement that ended decades of conflict.
Irish Prime Minister Leo Varadkar told reporters in Dublin that the Brexit talks had moved in the right direction.
"The initial indications are that we are making progress, that negotiations are moving in the right direction," he said. "But whether we will be able to conclude a revised withdrawal agreement, which after all is an international treaty, in time for the summit on Thursday, that's as of now unclear."
He added that some hours earlier the gap was "still quite wide, particularly on the issue of customs."
Varadkar said British Prime Minister Boris Johnson told him at a meeting last week that he was confident he could get a Brexit deal through the British parliament.
RISKS OF A NO-DEAL
If London is unable to clinch a deal, an acrimonious divorce could follow that would hit trade and business, roil financial markets and potentially lead to the United Kingdom splitting.
Even if he wins the approval of Europe's big powers, Johnson must still sell any deal to a British parliament in which he has no majority.
However, Steve Baker, the leader of a strongly pro-Brexit faction within Johnson's Conservative Party, said on Tuesday he was optimistic that "a tolerable deal" could be struck that he could vote for in parliament.
A leading figure in the 2016 referendum who came to power as head of ruling Conservative Party in July, Johnson has pledged to take the country out of the bloc on October 31 whether or not a withdrawal agreement has been reached.
But parliament has passed a law saying Britain cannot leave without an agreement and Johnson has not explained how he can get around that.
SATURDAY PARLIAMENT SESSION
The main obstacle is around customs, with London proposing that Northern Ireland stays in the UK customs area but that EU tariffs are applied on all goods crossing from mainland Britain to the island.
The EU has many doubts about the plan, saying the system is too complicated, untested and not detailed enough at this stage.
It believes the only possible deal to be had at the summit is a return to a 'backstop' solution - already rejected by Britain - of keeping Northern Ireland in the EU customs area.
It would require a major shift from London and Johnson will face parliament, which like the country as a whole is deeply divided over the issue, at a rare Saturday session.
"If there is to be a quick deal, it has to be based on the plan of Northern Ireland-only backstop," an EU diplomat said.
"It could be a mix of Northern Ireland-only and the customs partnership that had been proposed by (former British prime minister) Theresa May. With a lot of lipstick on it," said an EU official.