UK Prime Minister David Cameron has pledged to "battle hard for Britain right through the night" as he braced for a showdown with EU counterparts over his renegotiation demands.
The Prime Minister insisted he was confident of getting a "good deal" despite other leaders queuing up to dismiss his call for a four-year ban on in-work benefits for migrants.
He admitted there would be no agreement at the two-day Brussels summit, as had originally been hoped. Instead he said the gathering needed to put "momentum" behind the negotiations.
Speaking to reporters as he arrived, Mr Cameron pointed out that the EU Referendum Bill had received royal assent and the UK's in-out vote would definitely take place by the end of 2017.
"Tonight here in Brussels, we are going to have a conversation dedicated to Britain's renegotiation of its position in Europe, and I want to see real progress on all the four areas I have mentioned," he said.
"We are not pushing for a deal but we are pushing for real momentum.
"I am going to be battling hard for Britain right through the night.
"I think we will be getting a good deal."
Mr Cameron is under intense domestic pressure to secure substantial concessions for Britain ahead of the referendum on EU membership promised by the end of 2017.
Officials say he will make a "direct" and "constructive" appeal to counterparts over dinner, insisting they must respond to UK concerns about a lack of control over immigration, the effects of closer eurozone integration, the single market and a lack of competitiveness.
Mr Cameron, who will hold talks with Lithuanian and Greek leaders before the summit officially gets under way, is again due to raise the idea of the four-year ban - a Conservative Party manifesto pledge at the general election.
He has indicated he would be willing to consider alternative ways of cutting immigration "pull factors", although British officials say no other ideas have yet been tabled.
Speaking to reporters at the European Council building in Brussels, the body's president Donald Tusk said parts of the British demands seem "unacceptable".
He said: "The consultations I have led with all member states shows goodwill of all the parties involved, but it doesn't change the fact that some parts of the British proposal seem unacceptable.
"However, if Prime Minister Cameron persuades leaders tonight that we can work together to find solutions regarding all four baskets, then we will have a real chance to strike a deal in February."
Asked at a separate press conference whether there is any chance of getting the ban, European Commissioner president Jean-Claude Juncker said: "We will enter the concrete and vital phase of negotiations with our British colleagues, the Commission is ready to look for other options to the single one proposed by the British Prime Minister and I am quite convinced that we will find an answer to that highly complicated question."