Who are the EU out campaigners?

Britain's membership of the European Union is to be put to a public vote by the end of 2017. Here's a guide to the Eurosceptic groups campaigning for an exit, and the key players involved.

Rival groups

Two campaigns, Leave.EU and Vote Leave, have been launched in recent weeks to push for a UK exit from the EU.

Vote Leave was launched on 9 October 2015, and comprises a cross-party group of MPs and peers from the Conservatives, Labour and UKIP.

It is funded by people of different party affiliations including City millionaire and Tory donor Peter Cruddas, Labour's biggest private financial backer John Mills and Stuart Wheeler, a Tory-turned-UKIP donor.

Three Eurosceptic groups are backing Vote Leave:

Conservatives for Britain, created by Tory MP Steve Baker, whose president is Eurosceptic former Conservative Chancellor Lord Lawson. The group says the UK's current relationship with the EU is "untenable" and that while it has "every confidence" in David Cameron's ability to negotiate a better deal it is willing to consider campaigning to leave

Labour Leave campaign, spearheaded by Labour MPs Kate Hoey and Kelvin Hopkins (though almost all Labour MPs back Britain's continued EU membership)

Business for Britain, which wants big changes to the UK's relations with the EU and says the UK should be prepared to vote to leave if reform is not achieved. It has affiliated to the group but remains a separate entity. It recently published a 1,000-page report, called Change or Go, to make its case on EU reform.

Douglas Carswell, UKIP's only elected representative in the House of Commons, has broken ranks with his party leader to support the group.

Vote Leave is being run by Taxpayers' Alliance campaign group founder Matthew Elliot, who organised the successful 'No2AV' campaign in the referendum on reform of the Westminster voting system, and Dominic Cummings, a former special adviser to Conservative cabinet minister Michael Gove.

Leave.EU was formerly called The Know and rebranded when an amended referendum question was proposed. Founded by UKIP donor Arron Banks, it has the backing of party leader Nigel Farage, who billed it as an "umbrella group" of anti-EU campaigners.

It describes itself as "Britain's fastest-growing grassroots organisation" and claims to have gained 175,000 members since The Know was launched in August.

It will be up to the elections watchdog, the Electoral Commission, to designate which of the groups will become the official "Leave" campaign - though no decision has yet been taken. The chosen group (as well as the official "In" campaign) will benefit from increased spending limits of £7m during the campaign period, campaign broadcasts and a free mail-out to households. They all get access to public meeting rooms and to the electoral register, and are entitled to public grants of up to £600,000.

What have the camps said about each other?

Commenting on the launch of Vote Leave, Nigel Farage said he believed the two campaigns were aimed at "different audiences". He said Vote Leave was making "Westminster-based" business arguments but believed that Leave.EU would be able to reach outside to wider audiences.

Conservatives for Britain, which backs Vote Leave, received a less generous welcome from Leave.EU when it was launched. The group said Conservatives for Britain was "run by the Westminster bubble" and branded its leader, ex-chancellor Lord Lawson, a "has-been".

Mr Carswell said it was a "one-horse race" in favour of Vote Leave to become the official campaign, and dismissed the level of support for Leave.UK, saying: "Getting a whole bunch of likes on Facebook is not the same as winning a referendum."

Speaking as Vote Leave was launched, both Mr Carswell and Mr Farage talked up the possibility of a single campaign. UKIP's leader said the two campaigns were "complementary not contradictory" and that he hoped for "one campaign that operates on a number of levels". Mr Carswell told BBC News he believed it was "only a matter of time" before the two campaigns rolled into one.

Farage's role

The scale of the UKIP leader's involvement in the campaign to leave the EU has been the subject of much debate. Mr Farage has insisted he does not want to lead the official campaign, and some Eurosceptics fear he would be too divisive a figure to fill that role. He has however said UKIP will "take the lead" in the campaign to quit the EU.

The other side

The In Campaign, which makes the case for continued EU membership, is expected to be launched early next week. Its executive director is Will Straw, son of former Labour Home Secretary Jack Straw. Another ex-Labour minister, Lord Mandelson, could play a role in the campaign. Labour also has its own campaign to stay in the EU, led by former Home Secretary Alan Johnson.