Proposals for a new settlement for the UK in the European Union will be tabled tomorrow following "good progress" in talks on David Cameron's reform demands, Donald Tusk said.

The European Council president said he would put forward the plans on Tuesday ahead of a crunch summit of EU leaders on February 18-19.

But in a sign that the Prime Minister's hopes of striking a deal could still face problems, Mr Tusk acknowledged that "outstanding issues" remained.

Downing Street has acknowledged Britain still faces "a lot of hard work" to secure an acceptable deal on EU reform and to persuade the other 27 member states to sign up to changes.

Intensive negotiations have taken place between diplomats in Brussels to finalise a package to be put to the EU's 28 national leaders in time for an early in/out referendum.

Agreement in February is regarded as crucial if the referendum is to be staged before the summer holidays.

In a message on Twitter Mr Tusk said: "Tomorrow around noon I will table proposal for a new settlement for #UKinEU. Good progress last 24 hours but still outstanding issues."

Mr Tusk approved a 24-hour extension on Sunday after a meeting with the Prime Minister, which delivered what Number 10 termed a "significant breakthrough" over migrant benefits, but failed to reach agreement on a number of other areas.

He will now present EU leaders with his proposed solutions to the UK's concerns over migration, sovereignty, competitiveness and protection for non-eurozone countries, for discussion at the upcoming Council summit.

Downing Street said the PM had secured a significant assurance that a proposed "emergency brake" on welfare payments to EU workers could be triggered immediately after a vote to remain in the EU, on the basis of existing levels of immigration.

Mr Cameron's official spokeswoman insisted that Britain had made "substantial progress", but added: "There is more work to do in all four areas - more work in some areas than in others."

It remained unclear how the proposed emergency brake would operate and who would have the final say on when the measure could be activated and how long it would remain in effect.

The mechanism has been put forward by Brussels as an alternative to Mr Cameron's plan to impose a unilateral four-year curb which other member states ruled out as discriminatory and in breach of the freedom of movement principle.

The PM agreed to accept it as a "stop-gap" measure - on the condition he received assurances the existing pressure on the UK would meet the threshold to trigger it and it could remain in place.

One critical stumbling block is the UK's demand for it to be allowed to remain in place "long enough to resolve the underlying problem" - perhaps as long as seven years.

Supporters of British withdrawal from the EU dismissed the frantic round of negotiations - which saw the PM cancel a planned trip to Scandinavia last week for hastily-arranged talks with European Commission president Jean-Claude Juncker - as a choreographed display designed to convince voters that Mr Cameron has been forced to fight hard for significant concessions.

Ukip deputy leader Paul Nuttall said: "The theatrics and drama of David Cameron's sham renegotiation continues and he is playing us for fools."

But Mr Cameron's spokeswoman denied the wrangling was confected: "I wouldn't accept that at all. Look at the amount of hard work, time and effort the Prime Minister, other senior ministers and senior Government officials have had to put into this. Look at the work we have had to do with a number of other European countries who have raised concerns.

"These are significant, far-reaching reforms and that is why it is taking time."

Among the proposals currently on the table were reforms to prevent non-EU nationals using sham marriages with Europeans to maintain their right to remain in the UK, she confirmed.

But she denied suggestions that the UK was seeking a veto over further integration in the eurozone, insisting that Britain was instead asking for a mechanism to be created to ensure any concerns from non-single currency members are properly addressed.

"We have been clear throughout that it isn't about the UK being able to veto further eurozone integration," she said.

In a sign of Tory divisions over Europe, Conservative Nigel Evans (Ribble Valley) said he was likely to vote to leave the EU.

He told BBC Radio 4's World at One programme: "If the deal is that we are allowed to do it when we want, then yes, but if we have to phone a friend, indeed in this case 27 friends, to decide that we can put our foot on the brake, then no driver in their right mind would get into a car with those sorts of conditions."

The former Commons deputy speaker said he had hoped the negotiations would have been "more radical".

"I suspect that when it comes down to it that I'm going to be voting to leave the European Union."

Eurosceptic Tory Mark Pritchard (The Wrekin) said he feared quitting the EU would increase the dominance of France and Germany.

He told the programme: "If we were to withdraw from Europe, France and Germany would dominate foreign policy, dominate defence policy and I don't think even arch Eurosceptics that want to withdraw from Europe would want to see a more dominant France and Germany running Europe."

Former cabinet minister Peter Lilley (Hitchin and Harpenden) said a temporary emergency brake would lead to legal challenges.

"If I had asked my officials when I was responsible for this to introduce a measure like this I'm sure they would have told me to go away and think again," he told the programme.