European Council president Donald Tusk will table a draft proposal on a new European Union deal for Britain at noon on Tuesday, adding to expectations that the British referendum on EU membership will take place in June.
Senior EU officials representing the EU's 28 members gathered in Brussels on Monday after discussions between Mr Tusk and Mr Cameron ended without agreement on Sunday evening in London.
But while Mr Tusk said on Monday that “outstanding issues” still remained in the negotiations, there was growing optimism among EU officials that a deal would be brokered.
Presenting the text on Tuesday would then leave time for officials to analyse the proposal further ahead of a key EU summit on February 18th and 19th, though officials have not ruled out the possibility of another summit by the end of the month.
Mr Cameron is expected to brief the British cabinet on Tuesday morning on the progress of the deal, before visiting a number of EU capitals in the next two weeks, including a visit to Hamburg on February 12th, when he will discuss Britain's renegotiation with German chancellor Angela Merkel.
Among the key issues of contention is the "emergency brake" clause proposed by the EU, which would permit member states to curb benefits to migrants should their social security system be deemed to be under pressure. At issue is the duration of such a clause: while the European Commission is understood to have presented a two-year time frame that could be extended by a further two years, Mr Cameron is believed to have pressed for seven years.
Source of contention
The question of when the clause could be implemented is also a source of contention. A European Commission spokesman yesterday declined to confirm whether the EU had accepted that Britain would immediately qualify for the measure because its welfare system was already sufficiently under strain.
After months of negotiations and legal wrangling, the EU reached a breakthrough late last week by proposing the "emergency brake" clause. But problems also remain in relation to the prime minister's other demands, particularly his request to safeguard the interests of non-euro zone member states. France has long expressed its opposition to anything that could be perceived to interfere in euro zone decision-making.
Addressing the European Parliament in Strasbourg on Monday, European Central Bank (ECB) president Mario Draghi called for a deal to keep Britain in the EU.
"A solution that would anchor the United Kingdom firmly within the EU while allowing the euro area to integrate further would boost confidence," the euro zone's top official said in a surprise intervention. "Citizens and markets are too often unsure about our capacity to act jointly in a spirit of common responsibility. We should prove them wrong."
The ECB has previously expressed concern privately that any move by Britain to safeguard the interests of non-euro zone member states could jeopardise the stability of the currency.
