British Prime Minister David Cameron says he is "battling for Britain" as he faces stiff resistance over a number of changes he's proposing.
If those changes are not implemented, he says, Britain may leave the EU.
Omar Dabbagh reports.
There have been six summits in the past nine months involving the 28 members of the European Union.
The latest two day gathering in Brussels is the last for 2015, with Britain's future in the EU on shaky ground as it renegotiates the terms of its membership.
British Prime Minister David Cameron wants an agreement that can reduce immigration, improve business competitiveness in the EU, give the UK more sovereignty, and protect London's banks from the eurozone.
What's being called a "Brexit" is gaining popular support in the UK if Mr Cameron doesn't get the deal.
But David Cameron has declared he will "battle" to get agreement.
"Today is the day that our referendum bill has received royal assent, and so as a result our in-out referendum will be going ahead before the end of 2017. Now tonight here in Brussels we're going to have a conversation dedicated to Britain's renegotiation of its position in Europe and I want to see real progress in all of the four areas that I've mentioned. We're not pushing for a deal tonight, but we're pushing for real momentum so that we can get this deal done. So I'm going to be battling hard for Britain."
But Mr Cameron is facing stiff resistance on one key front.
The proposal to make immigrants from the other EU states wait four years before claiming "in-work" benefits in Britain has been widely criticised.
Many eastern Europe members claim it contravenes EU laws banning discrimination.
German Chancellor Angela Merkel says she's pushing to avoid a "Brexit", but has also offered the UK a stern warning.
"From the German point of view I will hold the debate in the spirit that we would like to keep Britain in the European Union but at the same time do not want to limit the basic liberties, non-discrimination, free movement, of the European Union."
Similar rhetoric was expressed by French President Francois Hollande.
Hungarian Prime Minister Viktor Orban says he believes it might take until next year until an outcome - one way or another - is reached.
"David Cameron's proposals have four major chapters. Three supportable, easy for us, basically we agree. The fourth one is more complicated so we should negotiate more on that. And that's exactly the social issue."
Britain's demands come as the EU continues to address a superabundance of new arrivals.
One million people have arrived in Europe this year alone, and proposals to boost the zone's external border forces are being considered.
President Hollande says he'll support that proposal, and the bid to resettle Syrian refugees directly from camps in Turkey, thus trying to prevent them taking boats across the Mediterranean.
"External borders must be protected. I absolutely agree with the proposal of the EU Commission to have guards at borders. We must also commit to respecting our word, especially for refugees that need to be moved or relocated but within the limits that were set."
Greek Prime Minister Alexis Tsipras believes a resolution to the crisis cannot be reached without greater solidarity across Europe.
"I think that now is the time for more cooperation in order to decrease migrant flows, and especially non-refugee flows, to have a constructive discussion today, also with the prime minister of Turkey, and we have to work harder in this direction. Greece had made its obligation, we made significant progress in the hotspots in the reception centres - I don't like this word 'hotspots'. We're ready to cooperate more closely with Turkey in order to decrease the flows but our first obligation is our humane obligation to give to these people solidarity."
