LONDON (AFP) - Prime Minister David Cameron is not expecting a deal at a summit this month in Brussels on his proposals to renegotiate Britain's EU membership ahead of a referendum, Downing Street said Thursday.
Although Cameron has vowed not to "take the foot off the pedal", it now looks as though the referendum on whether to leave the European Union will not take place until the second half of next year or even 2017, experts said.
In a statement issued after a call between Cameron and German Chancellor Angela Merkel, Downing Street said: "He noted that the scale of what we are asking for means we will not resolve this in one go and consequently he did not expect to get agreement at the December European Council."
Britain is still hoping for a "substantive discussion" of its demands at the Brussels summit on Dec 17 and 18, the statement added.
Speaking in Sofia, where he was holding talks with Bulgarian counterpart Boyko Borissov, Cameron said: "We won't take the foot off the pedal.
"We'll keep up the pace of negotiations and we'll use this summit to... work on solutions in the toughest areas because we do need reforms in each and every area I've set out."
The news came the day after European Council President Donald Tusk was quoted as saying that Cameron was aiming for a deal at the December summit.
"If he is ready to take this risk, I will be helpful. But then, it would be his risk," Tusk said in an interview published by several European newspapers.
"If Cameron is sure December is better for him as the organiser of this referendum, I will be helpful and I am ready to convince our officials."
Earlier in the year, British officials also indicated they thought a deal was possible at this month's summit.
However, a string of other issues are expected to dominate proceedings, which is being held in the wake of last month's Paris attacks that killed 130 people and an ongoing migrant crisis linked to the war in Syria.
Cameron last month formally laid out a list of Britain's demands to European leaders which includes a controversial bid to prevent EU migrants from claiming certain state benefits during their first four years in the country.
His spokesman confirmed earlier Thursday that this demand still formed a "core" part of Britain's renegotiation strategy despite opposition from countries like Poland which have a high level of migration to Britain.
The British leader has called the referendum a "once in a generation" choice and says he wants to stay in the EU subject as long as he can secure the changes he wants to Britain's relationship with Brussels.
However, Cameron has also warned he could call for Britain to leave the bloc if he does not get his way.
Britain's parliament is nearing the end of its debates on the legislation which will underpin the referendum, although pressure from the House of Lords to give 16 and 17-year-olds the vote could delay its passage into early next year.
Tim Oliver of the London School of Economics predicted that the referendum may take place in the second half of next year or even 2017.
"The chances of a referendum next spring are very slim because the legislation might not be in place in time," he told AFP.
"The earliest date for a vote is therefore next autumn, although that is far from ideal given it will compete for attention with such things as the US presidential election. That means we could be looking at a vote in 2017."
Opinion polling suggests that the British public are finely balanced on whether to remain in the EU or leave.