'No deal yet' in EU-UK talks

"Intensive work in next 24 [hours] is crucial," he added.

Cameron said in a statement that a draft version of the accord on how to change the terms of Britain’s EU membership is likely to be sent to EU leaders on Tuesday.

Sources say there is a breakthrough in one of the main sticking points - welfare rights for EU citizens.

Cameron wants to curb benefits for EU workers in Britain for four years, a step which, other countries say, is discriminatory and threatens free movement of labour, a cornerstone of EU integration.

Tusk went to the British capital to discuss possible compromises, including an "emergency brake” - a mechanism to let the UK temporarily suspend in-work benefits in the event of a sudden surge in immigration.

In a win for Cameron, the brake is now expected to be part of the draft deal.

"[The EU] Commission have tabled a text making clear that the UK’s current circumstances meet the criteria for triggering the emergency brake. This is a significant breakthrough," the British leader’s office said in a statement on Sunday.

Meanwhile, eurozone governance has emerged as a possible problem for negotiators.

France is concerned over Britain’s ideas on how to safeguard the interests of non-euro states amid deeper eurozone integration. Cameron wants to protect the City of London from eurozone decisions, including by being able to delay votes on sensitive issues in the EU Council.

French officials circulated a letter last week saying Paris opposes any kind of veto powers for non-euro countries, the Financial Times reports.

But Cameron’s office said on Sunday: "We want to ensure the enforcement mechanism is watertight, recognising that there must be ways to escalate an issue where we have concerns.”

It said it also wants to curb abuse of EU free movement, via “more substantive proposals, including closing back-door routes to Britain.”

Tusk's negotiating team remained in London to hammer out details in the next 24 hours.

The EU Council president will then assess the situation and decide whether or not there’s enough common ground to table the draft proposal, an EU source said.

Any deal agreed by Tusk and Cameron would still have to be backed by other EU states to come into effect.

EU leaders are to meet on 18 and 19 February to discuss the proposals.

A summit deal would allow Cameron to call a referendum on the UK's EU membership before the summer holidays.