David Cameron has given warning that he will reject any deal to keep Britain in the European Union if it fails to meet his country's needs.
The UK prime minister said on Thursday he is "battling for Britain" as he arrived at a crucial, two-day summit in Brussels which could determine the country's future within the 28-nation bloc.
"I'll be battling for Britain. If we can get a good deal I'll take that deal but I will not take a deal that doesn't meet what we need," Cameron said.
"I think it's much more important to get this right than to do anything in a rush, but with goodwill and hard work we can get a better deal for Britain."
WATCH: Is the European project collapsing?
Under pressure from eurosceptics in his own centre-right Conservative Party and media commentators, Cameron has demanded a series of policy changes that will return powers to London in the run-up to a referendum on whether to leave the EU.
The referendum could happen as soon as June.
Al Jazeera's Emma Hayward, reporting from Brussels, said: "Whatever Cameron leaves with here, he has to go and sell it to the Briitsh public.
"We know from the polls that a lot of people are still very undecided [on whether or not to remain in the EU]."
Speaking to Al Jazeera from the Belgian capital, Nigel Farage, leader of the far-right United Kingdom Independence Party, said Britain should leave the EU.
"Britain divorcing itself from this political union isn't just about Britain. I personally hope, very much indeed, that a Brexit would be followed by a broader conversation in Europe," he said.
OPINION: A happy new year for Europe?
"I would like to think in 10 years' time, we would have a [Europe] made up of democratic sovereign states trading together, co-operating together, working together, but without a flag, without an anthem, without an army and without a police force."
But countries such as France oppose special protections for countries such as Britain that do not use the euro.
Britain has been an increasingly half-hearted member over the past decades, staying out of both the common euro currency and the borderless Schengen zone.
Calls to remain
For his part, French President Francois Hollande says there should be no way that Britain can hold up intense EU co-operation in the future.
"I want Britain to stay in the EU. But I hope most of all that Europe can advance, can be stronger," he said on Thursday in Brussels.
"And that no chief of state or government could stop that. We cannot stop Europe from advancing."
In her remarks, Chancellor Angela Merkel said that it was in Germany's national interest for Britain to remain in the EU.
"I'm going into this debate with the position that we would like to do everything to create the conditions so that Great Britain can remain part of the European Union," she said.
Merkel said Britain is an ally for Germany in promoting competitiveness and free trade, and that Europe needs Britain's foreign and security policy commitment.
Source: Al Jazeera and agencies