The Brexit vote: Everything you need to know about the referendum

There’s only one day to the British referendum that will decide the U.K.’s relationship with Europe for generations to come—high time for a look at what will happen in the vote itself.

First, the big picture. The issue is whether the country should exit the European Union or stay within the bloc. The “Leave” camp argue the EU is a very different proposition to the European Economic Community that Britain joined in 1973. Since then, its scope has widened to cultural, judicial and other areas beyond that economic Common Market.

On the other side, the “Remain” camp argues that the U.K. gains in economic benefits, security and global influence from being a key member of a large bloc of nations.

Those are the two sides in the June vote. Below is an explanation of who is eligible to cast a ballot and the other “mechanics” of the referendum. When will the result be known? What will happen next? Here key things to know about the in/out vote over the issue widely known as Brexit.

What will the referendum question be?

The wording is:

“Should the United Kingdom remain a member of the European Union or leave the European Union?”

There are two options for voters: “Remain a member of the European Union” or “Leave the European Union.”

Coming up with a format wasn’t as straightforward as might be expected. The bill passed to allow the ballot to take place had a different question: “Should the United Kingdom remain a member of the European Union?” with a yes/no choice of response. But the original wording was changed after complaints that it was biasedin setting out only the “remain” option.

Voters in Wales will also see a Welsh version of the question on their ballot papers.

When is voting day, and when do the results come in?

Polling stations in England, Scotland, Wales and Northern Ireland will be open on June 23 between 7 a.m. and 10 p.m. local time, or 2 a.m. to 5 p.m. Eastern Time.

The ballot count is expected to start as soon as the polling stations close. The result should be known by early morning on Friday, June 24, though this depends on the circumstances in the 382 local areas where the count is being carried out.

The first set of results look likely to be released at 12:30 a.m. local time, the official Electoral Commission has said. About half of the counting areas are expected to have reported by 4 a.m., and about 80% by 5 a.m. They are expecting the final set of results at 7 a.m.

Who can vote?

Voters must be at least 18 years of age. Anyone who voted in May 5 local elections held in Scotland, Wales and Northern Ireland won’t need to re-register for June 23’s referendum.

Figures showing how many people have signed up to vote will be released somewhere around five days before the referendum. This is who is eligible to vote in person or via mail:

• British and Irish citizens living in the U.K.

• British and Irish citizens who live overseas—any country, not just in the EU—who have registered to vote in the U.K. in the last 15 years

• People from the Commonwealth who have permission to enter or remain in the U.K.

The Commonwealth is an organization of 53 countries that mostly were formerly part of the British Empire. That means Indians, Australians and South Africans, for example, who are U.K. residents will be among those going to the ballot box.

And while Fiji and Zimbabwe have been suspended from the Commonwealth, people from those countries who live in the U.K. can still take part in the referendum.

• But people from the EU who reside in the U.K. won’t be able to vote, apart from citizens of Malta, Cyprus and Ireland.

While people can vote by mail, one instance shows there may be risk in that. Some Britons who live in Germany and France have run into difficulties sending their prepaid Brexit ballots back to the U.K.

What do the opinion polls say

Wednesday is the final day of campaigning for the referendum, and more polls are expected to be released.

In the latest batch of surveys, ORB for the Telegraph showed 53% of respondents back EU membership, compared with 46% who want to cut ties. But YouGov for TheTimes newspaper showed Brexit support has a two point lead, at 44% to 42%. An Survation poll for IG Group put the Remain camp at 45% and the Leave camp at 44%.

A recent run of polls had overall shown a narrow resurgence in support for the U.K. staying in the EU. There had been increased focus on polls following the murder of British lawmaker Jo Cox. Cox, who was a vocal supporter of the remaining in the EU, was killed one week before the referendum.

The “outcome of the referendum is on a knife-edge and is likely to fall in between the divergent outcomes being anticipated by phone and internet polls,” said NatCen, which released its own poll results Monday, in a statement.

Credit Suisse

Electoral districts in Scotland, Northern Ireland and parts of London appear the least likely to vote for a Brexit, says Credit Suisse.

What’s at stake?

Trade agreements, immigration and labor rules, travel regulations and financial transactions are among a host of issues that would have to be renegotiated by British and European officials if the majority of Britons vote for the U.K. to leave the 28-member European Union.

Last year, 44% of exported goods and services from the U.K. went to the EU, representing 12% of Britain’s gross domestic product, according to the Office for National Statistics.

The pound GBPUSD, +0.1365%  has been the investing vehicle of choice for investors preparing for the vote. Sterling earlier this year hit a seven-year low against the U.S. dollar DXY, -0.31% trading below $1.39, on the prospect of a U.K.-EU breakup.

Read: Mohamed El-Erian on how a Brexit could solve a fundamental EU problem

The pound has since recovered to see trades above $1.47. But as shown above, the race could be close—and the polls have been wrong before. Last year’s general election was expected to be too close to call, only to have the Conservative Party quickly win an outright majority in parliament.

Who’s backing “remain” in EU?

• Prime Minister David Cameron is leading the Conservative government’s efforts in campaigning hard to stave off a Brexit.

The Conservatives—also known as “Tories”—are seen as having been cornered into holding the referendum by anti-EU Tory party members and by political pressure from the popularity of the euroskeptic UK Independence Party. The Brexit issue has caused a bitter fracture in the Tory party, as individual lawmakers have been given free rein to back whichever side they want.

Here are others who have picked this side:

• An array of high-profile organizations have said a Brexit would be a risk to the U.K. economy, including the International Monetary Fund, G-7 finance leaders, the U.K. Treasury and the Organization for Economic Cooperation and Development.

• President Barack Obama is a proponent of Britain staying in the EU, as are German Chancellor Angela Merkel and French President François Hollande. Spanish Prime Minister Mariano Rajoy has said a Brexit could affect the rights of Britons living in his country.

See: It isn’t just Brexit— Greece, Spain, France also on the brink

• Meanwhile, 250 British celebrities, including former “Top Gear” host Jeremy Clarkson and actress Keira Knightley, have come out against leaving the EU. U.S. actor and Oscar winner Matt Damon has called Brexit an “insane idea”. Soccer star David Beckham is backing the remain side.

• Stephen Hawking is among the 150 top scientists who have spoken out publicly for staying in the EU, saying to leave would “spell disaster.”

Who’s backing “leave”—for a Brexit?

Conservative politician and former London Mayor Boris Johnson is campaigning for the U.K. to cut ties with the EU—seen by some as positioning before a challenge to Cameron for the Tory leadership.

Stars in favor of a Brexit include actor Michael Caine, actress Joan Collins, rock star Noel Gallagher of Oasis and “Downton Abbey” creator Julian Fellowes.

As well, 250 business leaders have lent their support to the cause, including the former chief executive of banking giant HSBC HSBA, +0.16% HSBC, +1.34%Michael Geoghegan.

See:Pro-Brexit economists make case for U.K. departure

U.S. Republican-presidential nominee Donald Trump says he thinks the U.K. would be “better off” without the EU. Trump is scheduled to visit his Trump Turnberry golf resort in Scotland the day before the Brexit vote takes place.

Pub company J.D. Wetherspoon PLC JDW, +0.56%  has printed 200,000 beer mats laying out arguments for a departure, with Greece’s bailout and IMF governance among them.

What happens next, if voters choose a Brexit?

If the “leave” side wins, Prime Minister David Cameron said he’ll start working on the exit negotiations straight away.

He will first need to notify the European Council of the U.K.’s decision to withdraw, as called for under Article 50 of the Lisbon Treaty, the international agreement that underpins the EU. From this point, the U.K. won’t be able to take part in EU decision making.

Once that declaration has been made, talks will begin between the British government and the European Commission to define the U.K.’s new relationship with the EU. These will likely cover issues such as access to the single market, immigration and agricultural policy, and there is a two-year time limit for completing them.

This puts the U.K. on the back foot in the talks, somewhat. If it rejects the deal offered by the other 27 members of the EU, there is a chance that those other nations could let the clock run down. The U.K. might then find itself exiting on those terms anyway.

Read:How Cameron could use the vote against Brexit to change Europe

Keep in mind: Article 50 has never been used, so the political waters will likely be rough for the U.K. and the EU to navigate. Expect to hear chatter about pressure for Cameron, who promised to hold the Brexit vote if the Tories won last year’s general election, to resign his post. But the prime minister has already said he won’t give up his job.