The UK will vote on whether to remain in the EU on Thursday 23 June, Prime Minister David Cameron has said.
The prime minister made his historic announcement in Downing Street after briefing the cabinet.
He said he would be campaigning to remain in a reformed EU – and described the vote as one of the biggest decisions “in our lifetimes”.
Ministers immediately divided up into the leave and remain camps as the campaigns got under way in earnest.
Home Secretary Theresa May heads the list of those who announced they will campaign to stay – but Justice Secretary Michael Gove has signed up to the leave campaign.
London Mayor Boris Johnson, who was not at the cabinet meeting, has yet to declare where he stands.
‘Source of instability’
The referendum announcement comes after a reformed deal renegotiating Britain’s relationship with Europe was finalised on Friday night after intense wrangling at a two-day summit in Brussels.
In his statement, Mr Cameron warned that leaving the EU would be a “leap in the dark” as he urged voters to back his reform deal.
“The choice is in your hands – but my recommendation is clear. I believe that Britain will be safer, stronger and better off by remaining in a reformed European Union.”
Image copyright Vote Leave
Image caption Ministers nail their colours to the Vote Leave campaign
Mrs May said the EU was far from perfect but “for reasons of security, protection against crime and terrorism, trade with Europe, and access to markets around the world” it was in the national interest to remain in.
Mr Gove said it had been the most difficult decision of his career to go against the prime minister but he believed “our country would be freer, fairer and better off outside the EU”. He added: “Far from providing security in an uncertain world, the EU’s policies have become a source of instability and insecurity.”
Commons leader Chris Grayling, another leave campaign backer, told the BBC’s Laura Kuenssberg: “I actually believe the EU is holding this country back. We cannot control our borders, limit the number of people who come here do trade deals.
“I do not believe we can take decisions in the national interest when we are part of the European Union.”
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Media captionChris Grayling: “I believe the European Union is now holding this country back”
He said the prime minister had “put in a Herculean effort to try to deliver change” to Britain’s relationship with the EU, but the “concessions” he had brought back from Brussels did not “give us the opportunity to take decisions in the national interest” without consulting Brussels.
Culture Secretary John Whittingdale, Work and Pensions Secretary Iain Duncan Smith, Northern Ireland Secretary Theresa Villiers and employment minster Priti Patel, who is not a full cabinet member but attends meetings, have also joined the leave campaign.
The rest of the cabinet joined Mr Cameron in the remain camp, including Business Secretary Sajid Javid – previously seen as a potential leave supporter.
Mr Cameron claims his EU reform deal will give Britain “special status” within the bloc – tackling concerns over migrants getting “something for nothing” from the benefit system and exempting the country from the EU drive for “ever-closer union”.
But critics say it does nothing to tackle high levels of immigration or take back powers from Brussels.
UKIP Leader Nigel Farage said: “The 23rd is our golden opportunity, let battle be joined. Mr Cameron keeps on telling us that Britain would be better in a ‘reformed Europe’. But he fails to point out that there is no reformed European Union on offer here. The prime minister’s EU deal is pathetic.”
Britain Stronger in Europe released a campaign video accusing leave campaigners of “utter hypocrisy” for attacking Mr Cameron’s deal, claiming that many of them have been calling for the same reforms.
The Labour Party is officially campaigning for Britain to remain in the EU, although a small group of the party’s backbenchers have joined the leave campaign.
Leader Jeremy Corbyn voted for Britain to leave the European Economic Community, as the EU was then known, in 1975 but has since changed his mind, arguing that “it brings investment, jobs and protection for British workers and consumers”.
He branded Mr Cameron’s negotiations a “sideshow” aimed at appeasing critics in the Conservative Party and said he had missed an opportunity to protect jobs and “stop the spread of low pay”.
Scotland’s First Minister Nicola Sturgeon said in a statement the SNP will be “leading the positive case to keep Scotland in the EU”.