The already slim chance that a Brexit deal would be agreed this month receded still further on Monday as another EU meeting ended without a breakthrough.
In London, Prime Minister Theresa May's spokesman said talks in Brussels went on overnight until the early hours Monday and would continue, but he warned: "There are still substantial issues to overcome."
A government source said a deal must happen by Wednesday if there is any chance of an extraordinary EU summit this month to sign the withdrawal agreement.
If there is no deal in November, the crisis could drag on until a regular EU summit on December 13.
This would dramatically curtail the time May will have to get any agreement past a rebellious British parliament before Brexit day on March 29.
As fears rose that the saga will end with Britain crashing out without a deal, the pound dropped to 1.283 dollars against 1.297 at Friday's close.
Briefing the 27 other EU member states, "Michel Barnier explained that intense negotiating efforts continue, but an agreement has not been reached yet", the European Council of member states said.
"Some key issues remain under discussion, in particular a solution to avoid a hard border between Ireland and Northern Ireland," it added in a statement.