UK to discuss Tusk draft with EU states

"We want to ask questions, clarify details," a diplomatic source said.

One of the key issues is curbing benefits for EU workers in Britain through an "emergency brake".

The EU Commission has already given the UK assurances that in their case circumstances persist that justify the brake.

Some eastern European countries, which have a large number of their citizens working in the UK, are worried that the emergency brake opens the door for other member states to cap or limit benefits for EU workers.

"We want to make sure that it does not open the door for other countries to restrict benefits for EU workers, we would like to see them spelling out why, on what evidence does the situation in the UK merits this brake, and make sure it is not only a political decision but has some footing in evidence," a source added.

The time frame over which the brake can be used is still up for negotiation, but that might only be decided by EU leaders at their summit later this month, where British prime minister David Cameron hopes to secure a deal to enable him to hold an EU membership referendum in his home country on 23 June.

For the time being, there is one more so-called "sherpa" meeting scheduled for next Thursday.

The British prime minister met with Slovak premier Robert Fico in London to discuss the UK-EU deal. Cameron will travel to Poland on Friday to lobby for the UK-EU agreement.

Polish prime minister Beata Szydlo said Thursday that her government "will do everything" to keep Britain in the EU, but called the benefit issue "a problem".

Also in London, Tusk and Cameron met on the sidelines of the Syria conference in London, where they took stock of the capitals' initial reactions so far.

Nobody appears to be happy with the proposals so far, indicating that an agreement may be hard to secure, even if the document is balanced.

'No new negotiations'

Tusk also met with German Chancellor Angela Merkel and other European leaders in London.

The French president, Francois Hollande, has made some tough comments, and has been active in making sure the UK does not secure a veto or an option to delay decisions made by the eurozone member states.

The package of EU reforms offered to David Cameron is non-negotiable and Britain will be offered no further concessions, the French President has said.

Hollande warned Wednesday evening that there would be “no new adjustments or new negotiations” to the draft package of measures.

“We want the United Kingdom to remain in the European Union,” Hollande told reporters in Paris, according to the AFP.

“The compromise that has been found will likely allow us to find solutions to problems that until now seemed difficult to resolve. But at the European Council there can be no new adjustments or new negotiations," Hollande said.

"We have reached a point that should give Britons the reassurances needed while respecting European principles,” he added.