David Cameron is mounting a fresh push to finalise the details of his EU reform package amid signs Brexit campaigners are struggling to find a 'big beast' to lead them.
The Prime Minister will meet EU counterparts on the margins of a London summit about the Syria crisis, before hosting European Parliament president Martin Schulz at Downing Street.
Despite the emergence of a draft deal on Tuesday, the tricky task still facing Mr Cameron has been underlined by suggestions that MEPs could delay introduction of a so-called "emergency brake" on migrant benefits for 18 months.
He was also given a rough ride by a series of Tory backbenchers in the Commons on Wednesday, with Jacob Rees-Mogg complaining they were being offered "thin gruel".
Mr Cameron acknowledged further work will be needed to secure reform in an "intense" round of negotiations ahead of the February 18 EU summit.
In a round of broadcast interviews, the premier said he had "sorted" two welfare pledges, to deny EU migrants unemployment benefit and require them to return home after six months if they do not find a job.
Having promised to ban migrants from accessing welfare for four years, he argued he had achieved "four years until full access".
Mr Cameron also insisted that, while he had not secured a ban on child benefit payments to offspring abroad, it would be paid at local rates rather than the more generous UK level.
"I would say judge me on those things," he said. "They are substantial, they are meaningful. They are not the final word, but I think they do make a difference, particularly on this key value that we don't believe in something for nothing."
Former defence secretary Liam Fox has suggested up to five Cabinet ministers could back Brexit in the looming referendum - now regarded as almost certain to be held on June 23.
They are thought to include Work and Pensions Secretary Iain Duncan Smith, Leader of the House Chris Grayling and Northern Ireland Secretary Theresa Villiers.
But No10 will have been heartened by the apparent unwillingness of both London mayor Boris Johnson and Home Secretary Theresa May to throw their weight behind Leave.
Justice Secretary Michael Gove and Foreign Secretary Philip Hammond also look set to fall into line behind Mr Cameron.
Two rival groups - Vote Leave and Leave.EU - are engaged in a bitter battle to be designated as the official Brexit campaign by the Electoral Commission.
Vote Leave, which has been suffering from a bout of internal squabbling, last night announced a shake-up of personnel in a bid to draw a line under the problems.
Former chancellor Lord Lawson has been installed as chairman, replacing businessman John Mills, while campaign director Dominic Cummings and chief executive Matthew Elliott have both stepped down from the organisation's board in a move a spokesman claimed was "previously planned".
Arron Banks, founder of Leave.EU, suggested the changes could have removed the obstacles to a merger between the bodies.
But Tory MP Steve Baker, chairman of the Conservatives for Britain group, told BBC2's Newsnight that was "impossible".
"There are no plans for a merger. I believe Vote Leave will win the designation, I believe Vote Leave will win the referendum," he said.
"I don't think it is possible ... The reason is there are genuine disagreements over strategy and tactics."
Mr Baker said he would be happy to go into the referendum campaign with the team of politicians who are already backing Brexit, likening them to Shakespeare's "happy few".
However, he admitted he wanted to see more sign up, joking that his "dream" was for Mr Cameron to lead the Leave side.
Asked about reports that Mr Johnson was ready to support Remain, he said people "shouldn't believe everything they read".
James McGrory, chief spokesman for the Stronger In campaign, said: "Vote Leave have spent two days talking about emergency brakes, but it is clear the wheels have come off their chaotic campaign.
"Sacking three board members and demoting their chairman is the sign of a flailing organisation which reacts to losing the argument by shuffling the deckchairs."