EU leaders have agreed a deal in Brussels which will pave the way for an in/out referendum in the UK before the summer.
The development came late on the second day of gruelling talks in Brussels between leaders of the 28 member-states, which saw Prime Minister David Cameron face opposition to proposals to restrict migrant benefits and provide new protections for countries outside the single currency.
Cameron confirmed the news on Twitter.
The development was first broken by Lithuanian president Dalia Grybauskaite, who herself send a tweet from the round-table discussions.
And minutes later, the breakthrough was officially confirmed by European Council president Donald Tusk.
She was followed by Danish PM Lars Lokke Rasmussen.
The agreement clears the way for David Cameron to return immediately to London and call a special Cabinet meeting on Saturday to endorse the deal and set a date for the long-awaited referendum – widely expected to come on June 23.
The meeting will also give a green light to Eurosceptic ministers like Iain Duncan Smith and Chris Grayling to go out and campaign for Britain to leave Europe, and put pressure on waverers like London mayor Boris Johnson and Cabinet minister Michael Gove to spell out where they stand.
Sources close to Gove declined to comment on increasingly confident reports that the Justice Secretary is preparing to throw his weight behind Brexit.
The deal came after behind-the-scenes talks which stretched through Thursday night and most of Friday, as Cameron and Tusk struggled to keep Britain’s renegotiation on track.
The 28 leaders had initially been due to gather early in the morning for an “English breakfast” meeting to approve a package of reforms to the UK’s membership, but breakfast became brunch, lunch, high tea and then dinner as opponents of the deal dug in their heels.
The delays forced Cameron to scrap plans to summon ministers for a Cabinet meeting on Friday evening.
Cameron had faced concerns from eastern European countries like Poland, Hungary, the Czech Republic and Slovakia over his call for an “emergency brake” on in-work benefits for migrant EU workers to extend for as long as 13 years.
And the same nations put up stiff resistance to the UK’s demand to impose cuts in child benefits for offspring living abroad on 34,000 existing claimants as well as future migrants.
Meanwhile, France and Austria voiced anxiety that the protections for non-euro states sought by Cameron might effectively grant special status to the City of London and allow Britain to hobble any future deepening of the eurozone.