But eurosceptics in Britain dismissed the proposals as worthless, and they could be a hard sell ahead of the February 18-19 summit for some EU states, who fear that Cameron is winning too many concessions.

“To be, or not to be together, that is the question which must be answered not only by the British people in a referendum, but also by the other 27 members of the EU in the next two weeks,” Tusk said in a letter to EU leaders.

Tusk later warned that a deal was not certain in the pre-summit negotiations, which will begin in earnest on Friday when EU diplomats meet in Brussels.

“It’s still a lot of work ahead of us. The stakes are really high,” Tusk told the BBC. “Nothing is easy in this case.”

US President Barack Obama waded into the debate on Tuesday, calling Cameron to reiterate his support for “a strong United Kingdom in a strong European Union,” according to the White House.

Washington has long backed Britain playing a central role in the world’s largest economic bloc.

London’s bid to transform its EU membership has added to the turmoil in the bloc as it struggles with its worst migration crisis since World War II and the fallout from the eurozone debt saga.

As part of a charm offensive, Cameron will visit Poland and Denmark on Friday then Germany next week for talks with Chancellor Angela Merkel.

On Wednesday he will also set out details of the plan to parliament in London, his first opportunity to test reaction to the draft deal.

The British premier said Tusk’s proposal showed that he had “secured some very important changes”.

“If I could get these terms for British membership I sure would opt in for being a member of the EU,” Cameron said in a speech in southwest England.

Tusk’s most controversial proposal is an “emergency brake” that would allow any EU state to limit the welfare payments migrants from other European countries can claim for up to four years after their arrival.

To pull the brake, states would have to prove an “exceptional situation,” in which their welfare system and public services are overwhelmed, get approval from the European Commission, the EU’s executive arm, and then from other bloc leaders in a majority vote.

But instead of Cameron’s demand for an outright ban, such limitations should be gradually reduced over the four years.

Czech Europe minister Tomas Prouza said the welfare brake plan was “acceptable,” striking a more positive note after central European countries voiced concern the scheme would discriminate against their citizens working in Britain.

But British eurosceptics were unconvinced, with London Mayor Boris Johnson, from Cameron’s own Conservative Party, saying he had “doubts” about their effectiveness.

UK Independence Party head Nigel Farage dismissed Tusk’s proposals as “pathetic” and “hardly worth the wait”.