[LONDON] No deal was reached between British Prime Minister David Cameron and European Union President Donald Tusk Sunday in talks to agree changes to Britain's membership of the bloc ahead of an in-or-out referendum.
"No deal yet. Intensive work in next 24 (hours) crucial," Mr Tusk wrote on Twitter following a working dinner of salmon, beef and vegetables in Mr Cameron's Downing Street office in London.
Mr Cameron is pushing to exclude European Union migrants from benefits such as income top-ups for low-paid workers until they have paid into the British system under a so-called "emergency brake" system.
A spokeswoman for Cameron said that "much progress" had been made since a Friday meeting with European Commission chief Jean-Claude Juncker.
The Commission has indicated that Britain's "circumstances meet the criteria for triggering the emergency brake" - which would require countries to argue that their welfare system was under strain.
"This is a significant breakthrough, meaning the prime minister can deliver on his commitment to restrict in-work benefits to EU migrants for four years," the spokeswoman said.
"But there are still areas where there is more to do and both agreed it was therefore worth taking the extra time to make further progress."
The Conservative leader has vowed to secure reform in four key areas to address the concerns of British people with doubts about EU membership, before campaigning to remain within the 28-member bloc in a referendum due by 2017.
The EU source said that Mr Tusk would "assess the situation" after 24 hours before deciding whether or not to take the deal to other EU countries for consideration.
British officials hope that a final deal can be nailed down at a Brussels summit on February 18 and 19, which Mr Cameron would then use to campaign for Britain to stay in the bloc.
An agreement at that time would open the door to a referendum in June, but Mr Cameron insists he is willing to hold out for as long as it takes to secure the right package of reforms, if necessary delaying the referendum until September or even next year.
Underlining the challenges ahead, France warned Britain that it would block a separate proposal to allow one country about to be overruled in a vote the ability to pause the process.
"To French officials, any provisions giving non-euro countries power to indefinitely stall eurozone votes are unacceptable," the Financial Times reported, saying that France would refuse any "backdoor veto" for the City of London finance hub.
The talks in London were to cover all four areas in which Mr Cameron wants reform: migrant benefits, safeguards against more political integration in the EU, protection of countries such as Britain which do not use the euro currency and boosting economic competitiveness.
According to government sources Mr Cameron is prepared to accept the "emergency brake" in place of a previously proposed four-year curb on EU migrants claiming benefits, which other countries had objected to as discriminatory and which could require a treaty change.
"The prime minister intends to leave Tusk in no doubt that he will not do a deal at any price," a senior government source said.
Mr Cameron wants the "emergency break" to come into force immediately after a referendum in favour of membership, in a bid to reduce what the British government considers a "pull factor" encouraging Europeans to come to the UK in search of work.
The number of European job seekers has become a hot political issue in Britain and key driver of anti-EU sentiment.
Mr Cameron is under increasing pressure from his own centre-right Conservative party, which has a strong eurosceptic contingent, to come back with a robust deal.
Opinion polls currently suggest that Britons would vote to leave the EU in a so-called "Brexit" by a small margin.
Reflecting domestic pressure on Mr Cameron, the co-chair of the anti-EU Conservatives for Britain group dismissed the talks as "synthetic" and a "farce".
"It is not going to answer the concerns of the British people. We need the power in our own parliament to determine what our migration policy is," he told Sky News.