Key Voices in Britain's EU Referendum Debate

The rival campaigns for Britain to leave the European Union or stay part of the 28-member bloc are taking shape ahead of the June 23 referendum.

Here are the key players in the debate:

- The “Remain” camp -

- Prime Minister David Cameron: He is leading the campaign for Britain to stay in the European Union. Most of his Conservative MPs will fall into line, but media reports suggest at least a third of the party's 330 lawmakers could vote against.

- Jeremy Corbyn: The main opposition Labor party has said it will campaign to stay, although a few euroskeptics there too will decide to vote against.

Corbyn, the party leader, has branded the reforms Cameron secured in Brussels as a "sideshow" but has said he will campaign to stay because of investments, jobs and worker protection from the EU.

- Nicola Sturgeon: Scotland's first minister and the head of the pro-independence Scottish National Party has said she will be at the "forefront" of efforts to stay in, warning that a so-called Brexit could trigger a second vote for Scotland to leave the United Kingdom.

- Campaign: "Britain Stronger in Europe" is the main group advocating British membership. It is led by Stuart Rose, a former chairman of the retailer Marks & Spencer and a Conservative member of the House of Lords, but he has kept a low profile so far.

- Business: Key business leaders including Richard Branson have spoken out for EU membership, with the Virgin founder warning a departure would be a "very sad day". Barclays bank chairman John McFarlane has warned the City, Europe's premier financial hub, would be "significantly" worse off without the EU.

- Celebrities: Several cultural figures have come out as pro-EU. The latest, award-winning British actress and campaigner Emma Thompson, said leaving Europe would be "a crazy idea". "Of course I'm going to vote to stay in Europe. Oh my God, it would be madness not to," she told reporters at the Berlin Film Festival.

- Royals: Prince William never actually mentioned the word Europe but in a speech at the foreign ministry this month, the second in line to the throne made comments that were widely interpreted in British media as being in favor.

"Our ability to unite in common action with other nations is essential, it is the bedrock of our security and prosperity," he said.

- The “Leave” camp -

- Boris Johnson: With a popular appeal that reaches beyond his Conservative party, the charismatic mayor of London is likely to become the public figurehead of the campaign.

- Ministers: Five of the cabinet's 22 members back Brexit: justice minister Michael Gove, work and pensions minister Iain Duncan Smith, Northern Ireland minister Theresa Villiers, sports and media minister John Whittingdale and Chris Grayling, the cabinet's representative in parliament. Junior minister Priti Patel, who attends cabinet, joins them.

- Nigel Farage: The head of the anti-EU UK Independence Party (UKIP), who is a member of the European Parliament but failed to get elected to the British parliament last year, has advocated for Britain to leave the EU all of his political life.

He greeted news that a referendum date had been set by declaring: "Let battle be joined. We want our country back." He said life outside Europe would mean "control of our borders, global trade deals, making our own laws. An exciting future".

- Campaign: Various movements have been set up to advocate Brexit from both the right and the left -- among them "Vote Leave", "Labor Leave", "Leave.EU". Relations between them have sometimes been tense and only one can win official designation by the electoral commission, which brings with it a higher spending limit and public funds.

- Business: Some entrepreneurs have spoke out for Brexit, including vacuum cleaner tycoon James Dyson.

The inventor was quoted by the Daily Express as saying that he did not want to stay in a Europe "dominated and bullied" by Germany.

- Celebrities: Only very few cultural figures have declared public support for Brexit. Oscar-winning actor Michael Caine told the BBC that Britain should leave if it does not manage to negotiate "extremely significant changes". "I sort of feel certain we should come out," he said.