By Bill Smith

London (dpa) - Prime Minister David Cameron on Saturday urged voters to say "yes" in a historic referendum on whether Britain should remain a member of the European Union, but he faced growing opposition within his own Conservative party.

"We are approaching one of the biggest decisions we will face in our lifetime - whether we want to remain in the European Union or leave," Cameron told reporters as he announced plans for a referendum on June 23.

The decision "goes to the heart" of the nation's identity, he added after meeting with his ministers to discuss a reform deal reached with leaders of the other 27 EU nations late Friday in Brussels.

"I do not love Brussels, I love Britain," Cameron said.

"The question is, will we be safer, stronger and better off ... working together in a reformed Europe," he said. "I believe Britain will be stronger in a reformed Europe."

"Leaving Europe would threaten our economic and our national security," Cameron said, urging people not to take a "leap in the dark" by voting to leave.

Cameron said he had secured a deal to give Britain a "special status" in the EU, offering the "best of both worlds."

But he faces growing dissent from Conservative politicians, with six of his own ministers joining a Vote Leave event on Saturday.

London Mayor Boris Johnson, one of the Conservatives' most popular figures, stayed on the fence during the negotiations and is expected to announce his decision on which campaign to support on Sunday.

Leading Saturday's dissenters was Justice Secretary Michael Gove, who said he believes Britain "would be freer, fairer and better off outside the EU."

"Far from providing security in an uncertain world, the EU's policies have become a source of instability and insecurity," Gove said.

"This chance may never come again in our lifetimes, which is why I will be true to my principles and take the opportunity this referendum provides to leave an EU mired in the past and embrace a better future," he said.

At least 65 of the 330 Conservative members of parliament have declared their support for a British exit, or Brexit, and many others are expected to follow.

But Cameron's campaign for Britain's continued EU membership is boosted by strong support from Labour and the Scottish National Party - despite most opposition politicians dismissing Friday's deal as mainly designed for Cameron to rally Conservative eurosceptics behind him.

"Despite the fanfare, the deal that David Cameron has made in Brussels on Britain's relationship with the EU is a sideshow, and the changes he has negotiated are largely irrelevant to the problems most British people face and the decision we must now make," Labour leader Jeremy Corbyn said.

"His priorities in these negotiations have been to appease his opponents in the Conservative party," Corbyn said.

"He has done nothing to promote secure jobs, protect our steel industry, or stop the spread of low pay and the undercutting of wages in Britain," he said.

Nigel Farage, leader of the anti-EU UK Independence Party, said the deal - which allows Britain to restrict EU migrants' welfare benefits and opt out of an obligation to build an "ever closer union" - was "not worth the paper it's written on."

The Confederation of British Industry welcomed the reforms and said they "protect the UK's place and influence inside this important market."

"Most CBI members - though not all - have told us that being in a reformed EU is better for jobs, growth and prosperity," said Carolyn Fairbairn, the CBI's director general.

A leading German representative in the European Parliament said that other countries could also benefit from the planned reforms, which would only come into effect if Britain's votes to stay in the bloc.

"The fact that future child benefit payments for children living elsewhere in the EU can be adapted [in line with the country in which they live] can be a benefit to all 28 member states," said Herbert Reul, who leads Chancellor Angela Merkel's centre-right Christian Democrats in Brussels.

Merkel had previously said herself that Germany may be interested in adopting this new rule, which could see a reduction in child benefits to EU workers whose families live abroad.