UK and EU officials will resume talks on Monday with the prospects of a Brexit deal apparently finely balanced.
The EU’s chief negotiator Michel Barnier has said “technical-level” talks over the weekend had proved “constructive”.
But in a briefing to ambassadors of the remaining EU27 in Brussels on Sunday, he said that “a lot of work remains to be done”.
Earlier Prime Minister Boris Johnson told senior ministers that while a “pathway” to a deal could still be seen, there was “still a significant amount of work to get there”.
In a Cabinet conference call, he said that they still had to be prepared to leave without a deal on October 31.
The assessments came amid reports from the Belgian capital that the chances of getting an agreement in time to be signed off by Thursday’s summit of EU leaders were looking increasingly slender.
The more downbeat mood was in contrast to the burst of optimism which followed Mr Johnson’s meeting last week with Irish premier Leo Varadkar on the Wirral.
The sticking point remains the issue of the Northern Ireland backstop, intended to guarantee there will be no return of a hard border with the Republic.
A reported attempt by the UK side to revive a compromise proposal by former PM Theresa May for a “customs partnership” between Northern Ireland and the EU was said to have run into opposition from both Brussels and Mr Johnson’s allies in the DUP.
Earlier Jacob Rees-Mogg appeared to be softening up Brexiteers for possible concessions, warning that some compromise was “inevitable” in the closing stages of any negotiation.
The Leader of the Commons – who was a thorn in the side of Mrs May over Brexit until he joined Mr Johnson’s administration – said they could “trust” the Prime Minister not to give too much ground.
“I think that he is somebody who even the arch Eurosceptics, even a member of the Brexit Party, can trust and have confidence in,” he told Sky News’ Sophy Ridge on Sunday programme.
If Mr Johnson cannot get an agreement by the weekend, he will come under intense pressure to seek a further Brexit delay – something he has vowed not to do.
Labour, however, has warned that if necessary it will take action through the courts to force him to comply with the so-called Benn Act, which requires the Government to request an extension.
Either way, the stage is set for a major Commons showdown when the Prime Minister returns to Westminster for an emergency Saturday sitting of Parliament, the first in 37 years.
If he cannot get deal, he is widely expected to blame MPs for cutting the ground from under him, paving the way for a “people versus Parliament” general election.
If he is able to get an agreement, Government sources have said they will seek to rush through legislation to ratify it in time for the promised Halloween withdrawal date.
Some opposition MPs have signalled they could support an agreement if there was a requirement to put it to the public in a confirmatory referendum.
However, Labour leader Jeremy Corbyn indicated he had little enthusiasm for the idea.
“I think many in Parliament, not necessarily Labour MPs but others, might be more inclined to support it (if there was a referendum) even if they don’t really agree with the deal. But I would caution them,” he told Sophy Ridge on Sunday.