Millions of Britons voting in historic EU referendum that will shape British-EU ties for generations.
Millions of Britons are voting to decide whether the UK will remain a part of the European Union in a referendum that has divided the nation.
A record 46.5 million voters have signed up to weigh in on Thursday's referendum, which asks one, single question: "Should the United Kingdom remain a member of the European Union or leave the European Union?"
The divisive referendum has sparked the greatest emergency in the EU's 60-year history.
The vote pits the Remain campaign, backed by British Prime Minister David Cameron and opposition Labour Party leader Jeremy Corbyn, against the Leave camp, led by the former London mayor, Conservative MP Boris Johnson.
Polling stations opened at 7am (06:00 GMT) and will close 10pm (21:00 GMT) local time.
PM Cameron and his wife Samantha cast their ballots early on Thursday at London's Westminster Central Hall.
Nicola Sturgeon, the first minister of Scotland, voted Remain at a polling station in Glasgow.
"I did so with head and heart because being in [the] EU is best for Scotland," she tweeted.
Rainstorms were expected to dampen turnout in London and other parts of southern England.
There are no official exit polls because polling experts say the lack of recent comparable votes in Britain could make the results less reliable.
Results from polling will, however, be released shortly after the ballots close.
Too close to call
A Populus poll, the final opinion poll carried out online ahead of the historic vote, gave the Remain campaign a 10-point lead over Leave. Populus said the survey of 4,700 people was carried out on Tuesday and up to midnight Wednesday night.
But on the eve of the historic vote, two polls – both conducted over the internet – put the Leave camp ahead by 1 or 2 percent.
Standing outside a fish-packing plant a day before the referendum, Leave camp leader Boris Johnson argued it was time to take back control of the UK's industries.
"You take back control and I think it will be a big, big moment for democracy in this country and around Europe," said Johnson.
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Desperate to inject some pro-Europe passion late in the day on Wednesday, the prime minister and his allies made appeals to older voters, urging them to think of their children rather than their own nostalgic views of their country.
"Think of one word that brings it all into one, which is 'together', because frankly if we want a bigger economy and more jobs we're better if we do it together," said Cameron.
"If we want to fight climate change, we're better if we do it together. If we want to win against the terrorists and keep our country safe, we're better if we do it together."
The Remain camp has said a British exit would be hugely destabilising in terms of security and the economy.
Supporters of the Leave campaign argue that a Brexit would be for the best; much of its campaign focused on tighter border controls and freedom from EU regulations on immigration and the economy.
'Divisive, vile campaign'
There is also concern about the divisive impact of the campaign, in particular the pro-Brexit camp's focus on immigration.
The Mirror newspaper, which supports a "Remain" vote, has described it as "the most divisive, vile and unpleasant political campaign in living memory".
One of the most contentious posters of the campaign was one published by the anti-immigration UK Independence Party (UKIP), showing a long queue of refugees under the headline "Breaking Point".
The murder of Jo Cox, a passionate pro-European who had campaigned for Syrian refugees, brought only a temporary respite in the campaign.
Following her killing a week ago, the pound soared as several polls showed gains for the Remain camp, and it has kept its strength since. In early trading on Asian markets Thursday morning, Sterling reached its highest level of 2016.
"If we destroy the European Union, which for all its faults has nevertheless delivered a tremendous amount of cohesion within our continent, I think the consequences of that are fairly unpredictable. So for that reason, I don't think that's something we should wish for," Conservative MP and Remain campaigner Dominic Grieve told Al Jazeera.
'Out is out'
EU leaders have warned there will be no turning back from a vote to quit the 28-member bloc.
"Out is out," European Commission chief Jean-Claude Juncker said in Brussels, dismissing any chances of a post-vote renegotiation of Britain’s EU membership terms.
French President Francois Hollande has said an exit by the UK would be "irreversible".
The referendum has raised concerns across Europe that a British withdrawal could trigger a domino effect of exit votes and threaten the integrity of the bloc, already under severe strain from Eurozone and migration crises.
Even if it stays, the status quo will not be an option.
"Whatever the result is going to be, we must take a long hard look at the future of the union. We would be foolish if we ignored such a warning signal as the UK referendum," EU President Donald Tusk warned this week.
Tusk has previously said that a British leave vote could lead to the "destruction of not only the EU but also of Western political civilisation".
The EU was created after the Second World War as an antidote to the nationalism which had devastated the continent. The movement for unity was led by France and Germany.
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