Bilateral talks were still ongoing Friday afternoon (19 February) in Brussels among EU leaders and British prime minister David Cameron, with sources saying a deal is still likely this weekend between the UK and EU.
Overnight and early Friday, EU Council president Donald Tusk held several meetings with EU leaders and Cameron to close the remaining gaps on the key outstanding issues, such as eurozone governance, building an "ever closer union" in the EU, child benefits and restricting access to in-work social benefits in the UK for EU workers.
The so-called Visegrad Four, the Czech Republic, Hungary, Poland and Slovakia, are still at odds with the UK on how long the in-work benefits can be suspended for EU workers, with the UK's starting position at 13 years (7+3+3) and the eastern Europeans proposing seven years.
"We are waiting for Cameron to make a move, the V4 have already moved their starting position from 5 years to 7," a source said.
On the reduction of child benefits claimed by EU workers, a compromise could be found on non-retroactivity, meaning that only new workers will see their child benefits indexed to the cost of raising a child in their country of origin.
The measure granted to the UK would be optional for other EU countries. Denmark has already announced it would opt-in.
Representing the Visegrad countries, Czech prime minister Sobotka also met with German chancellor Angela Merkel to see whether Germany, another country with a large number of EU workers, might also look into curbing benefits for EU workers' children living elsewhere.
Poland is particularly worried that Germany might also opt-in to the child benefit indexation mechanism.
Polish sources said that any measures on child benefits in the UK and other EU countries could affect 100,000 Polish children, with 40 percent of them having parents working in Germany. The total number of eastern European children potentially affected is said to be 500,000.
Cameron met with Polish PM Beata Szydlo on the sidelines of the summit.
Some speculated that a package deal on child benefits and curbing in-work benefits could resolve the two issues.
Polish EU minister Konrad Szymanski suggested there was a compromise on the duration of benefits curbs, without revealing a number, and said the focus was on the child indexation issue.
Other outstanding issues remained, such as the reference to an "ever closer union", with Belgium insisting that the text make clear that no other country than the UK could free itself of this political commitment to deepen EU integration.
France was still asking for one word to be removed from paragraphs on EU powers in case of "threats to financial stability", to avoid that in the future Britain can be exempt from EU rules. It was also dragging its feet on incorporating the arrangement in an EU treaty change.
Cameron however made it clear to EU leaders on Thursday night that he could not accept any more concessions.
"As I've said I'll only do a deal if we get what Britain needs," he told reporters Friday morning.
Sources say bilateral meetings will go on until Tusk's team is ready with a new proposal, that would be discussed by leaders when they reconvene at 16.00 Friday afternoon. However, depending on the progress in the negotiations, the summit's schedule could be delayed.
"A deal is possible. But the timing depends on what kind of drama some countries like to perform," Lithuanian president Dalia Grybauskaite said.
When he arrived Friday morning, Cameron told reporters he had told his wife he might have to stay until Sunday. But diplomats said that some leaders were determined not to let Cameron impose his timing.
Describing the mood, a source said: "There is a sense that there will be a deal, might take longer, but the mood is there will be a deal."
As the "English meal", in which leaders were to discuss the UK proposals, was delayed once again, Belgian PM Charles Michel told reporters it was "now or never". "There won"t be a second chance," he said.
All previous sticking points remained unresolved when leaders broke for bilateral meetings at EU-UK talks Thursday night. Council chief Donald Tusk now has to "square the circle".
With tough political issues still outstanding, EU leaders gather in Brussels on Thursday where they will try to seal a deal with the UK that would help Cameron to campaign successfully for Britain to remain in the bloc.
Difficult discussions will take place over details on benefits and banking rules at the EU summit, amid efforts to find a way to keep the UK in the EU.
EU leaders have reached a deal on new UK membership terms after marathon talks in Brussels. The UK won concessions on a eurozone "brake" and welfare curbs.
British PM Cameron is due to make his case in parliament for the UK to stay in the EU, but party ally Boris Johnson has announced he will campaign to leave.