By William Schomberg and Ana Nicolaci da Costa
Prime Minister David Cameron has called a June 23 referendum on membership of the European Union as he sought to rally his divided Conservative Party behind a deal which he said would guarantee Britain's prosperity and security in the bloc.
After spelling out detail of the deal - clinched at an EU summit in Brussels - to his senior ministers, Cameron on Saturday (local time) said he had secured the cabinet's blessing to recommend to voters that Britain stay in the bloc it joined in 1973.
"I believe that Britain will be safer, stronger and better off by remaining in a reformed European Union," Cameron said outside his Number 10 Downing St residence in London.
"Leaving Europe would threaten our economic and our national security," Cameron said, adding that he would propose to parliament that the referendum be held on Thursday June 23, in the middle of the Glastonbury music festival and the Euro 2016 football championship.
One of Cameron's closest political allies, Justice Secretary Michael Gove, and five other cabinet members will campaign to leave.
They signed a poster for the Vote Leave out campaign saying "Let's take back control."
While the rebellion illustrated the depth of the division over Europe within his ruling Conservative Party, Cameron's most senior ministers including interior minister Theresa May and finance minister George Osborne backed EU membership.
London Mayor Boris Johnson, who has charmed some voters with a buffoonish persona that masks fierce ambition to succeed Cameron, has yet to make his position clear.
A source told Reuters that Johnson might show his hand on Sunday.
The agreement Cameron reached in Brussels granted Britain an explicit exemption from the founding goal of "ever closer union", offered concessions on the welfare rights of migrant workers and safeguards for the City of London.
Though British voters are split over membership, betting odds have moved further in favour of Britain remaining in the EU after Cameron's deal, according to bookmaker Ladbrokes.
A British exit from the EU would rock the Union - already shaken by differences over migration and the future of the euro zone - by ripping away its second-largest economy, one of its top two military powers and by far its richest financial centre.
Pro-Europeans warn an exit could also trigger the break-up of the United Kingdom by prompting another Scottish independence vote.
The US$2.9 trillion British economy would face years of uncertain negotiations over the terms of a divorce.
Opponents of EU membership say Britain would prosper outside what they say is a doomed Germany-dominated bloc that punches way below its weight on the world stage.
"This is a truly pathetic deal," Nigel Farage, the head of the UK Independence Party said. "Let's leave the EU, control our borders, run our own country and stop handing £55 million every day to Brussels."