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Millions entitled to a vote in the EU referendum could miss out because they are not on the electoral register, campaigners have warned.

Would-be referendum voters have until midnight on Tuesday 7 June to sign up to the electoral register.

Prime Minister David Cameron says more than a million people have done so since the referendum campaign began.

But figures suggest many people will leave it too late to register and will be turned away at polling stations.

Lib Dem peer Lord Rennard, chairman of the All Party Parliamentary Group (APPG) on Democratic Participation, said: "Many millions of people will not be on the register, and won't be able to take part in the referendum. Some, unaware of the deadline, will register too late.

"Before the last general election, 186,000 applied after the deadline. Despite the efforts of Bite The Ballot's #TurnUp campaign, this may happen again, and many people may think that they're already registered and turn up at the polls anyway."

An APPG report published in April, Missing Millions points to 2014 research which shows 7.1 million people have gone missing from the electoral roll and that the gap between the voting age population and registered voters is growing.

Registering to vote

British, Irish and Commonwealth citizens resident in the UK and many British citizens living abroad are entitled to vote in the referendum.

You can check with your local authority's electoral services team if you are worried that you are not on the register.

If you are not on the register you have until midnight on Tuesday, 7 June to submit an application for a vote. The deadlines for applying for a postal vote at the referendum are:

Northern Ireland - 5pm, Friday 3 June 2016

Great Britain - 5pm, Wednesday 8 June 2016

In England, Scotland or Wales, you can register to vote online anytime at gov.uk/register-to-vote. If you are a British citizen living abroad, you can register to vote online in the same way.

In Northern Ireland, visit the government's Register to vote in Northern Ireland page to download a registration form. If you are an Irish citizen living abroad who was born in Northern Ireland, visit the Electoral Office for Northern Ireland website to download the correct form.

Research by Dr Toby James, of the University of East Anglia, shows that many citizens think that they are on the register because they pay their council tax and therefore expect those running the election to "know about them".

The Missing Millions report shows that two thirds of polling stations turned away voters in 2015 who thought that they were on the electoral register, but were not.

Image copyright AP Image caption Coldplay are headlining Glastonbury - but there will be no referendum polling booths on the festival site

An Electoral Commission spokesman said: "There's only one way to ensure you're able to have your say at this historic referendum and that's to be registered to vote by 7 June.

"Anyone who was already registered to vote for the elections in May will be registered for the EU Referendum.

"If your circumstances have changed since May, for example if you've moved home, then you need to re-register at your new property."

Government figures show more than a million people have signed up to the electoral register since 1 March, with 25 to 34-year-olds leading the way. More than 25,000 people in that age group registered on Monday alone, out of a total for that day of 83,000. The next biggest group was the under-25s.

The figures show a big spike in applications for a vote on the deadline for registrations for May's elections in Scotland, Wales, Northern Ireland and English local authorities.

Image copyright Getty Images Image caption Campaigners are holding voter registration drives in coffee shops

But there was another, smaller spike on polling day itself, suggesting many people only discovered they were not on the register when they tried to vote and were turned away.

Campaign group Hope Not Hate and Bite the Ballot have launched a voter registration drive called #TurnUp with the aim of registering 500,000 young people by 7 June.

The campaigners are targeting universities, further education colleges, local neighbourhoods and faith communities and claim support from Facebook, Twitter and Tinder.

Bite the Ballot has also joined forces with Starbucks to hold voter registration and EU debate events at 50 coffee shops around the country, starting next Wednesday.

David Cameron highlighted the efforts being made to sign up younger voters at an event at Easyjet headquarters in Luton earlier on Tuesday.

"We are obviously doing a lot, encouraging companies and others to say this is a very big vote - it affects your future, it's not just about the next five years, it's about the next 50 years and I think over a million people have registered since this campaign started, which is very encouraging," said the prime minister.

Image copyright Reuters Image caption David Cameron is urging young people to sign up

Voters now have to register to vote as individuals rather than by household, as part of an attempt to cut down in electoral fraud.

Estimates vary as to how many people have "gone missing" from the electoral roll since a new system was introduced.

Millions of people were transferred automatically on to the new register after having their identity confirmed by checking social security and council tax records.

Names that could not be verified in this way were kept on the register until 1 December last year but have now been removed - a total of 770,000 entries. A total of 1.5 million people have been deleted since 2014, when the new system began to be rolled out but many could have signed up again since the figures were released earlier this year.

Labour's shadow minister for young people and voter registration, Gloria De Piero, said: "This referendum takes place at a time when we know 1.5 million people have been taken off the electoral register since the introduction of Individual Electoral Registration.

"You only have until 7 June to get on that register and have your voice heard.

"I hope everyone will think about where they will be on 23 June, so they can make sure they are registered at the right address.

"It might be easier to arrange a postal or proxy vote if you are going on holiday, to Glastonbury, or even if you will be studying hard for exams.

"We need everyone to play their part in the biggest decision of a generation."