Prime Minister David Cameron was to meet his cabinet on Saturday after securing a deal to give Britain a "special status" in the European Union, but he faced dissent from several ministers expected to join the "leave" campaign in a planned in-out referendum.
"The cabinet will this morning discuss the UK's new special status in the EU," Cameron said on Twitter. "Afterwards, I'll announce the planned referendum date."
The date of the referendum, in which voters will be asked to state whether or not they want Britain to remain part of the EU, is widely expected to be June 23.
After reaching agreement with leaders of the other 27 EU nations late Friday, following two days of intense negotiations, Cameron said Britain was "stronger, safer and better off inside a reformed European Union."
"Turning our back on the EU is no solution at all, and we should be suspicious of those who claim that leaving Europe is some automatic fast track to a land of milk and honey," he said.
Among the dissenters in his cabinet is Justice Secretary Michael Gove, who is set to announce his decision to join the "leave" campaign, according to the BBC and other British media.
Speculation surrounds a handful of other ministers who could join the campaign for a British exit, or Brexit, while at least 65 members of the 330 members of parliament from Cameron's Conservative party have declared their support for Brexit and many others are expected to follow.
Many opposition politicians dismissed Friday's deal - which allows Britain to restrict EU migrants' welfare benefits and opt out of an obligation to build an "ever closer union" - as mainly designed for Cameron to rally Conservative Eurosceptics behind him.
Cameron "has done what he decided he had to do because he was too weak to stand up to his political party," shadow foreign secretary Hillary Benn, whose Labour party supports Britain remaining in the EU, told the BBC.
Nigel Farage, leader of the anti-EU UK Independence Party, said the deal was "not worth the paper it's written on."