After months of campaigning, the "Leave" camp has won and Britain will be leaving the E.U. The Post's Adam Taylor talks about what that means for the country and Europe. (Adam Taylor,Jason Aldag/The Washington Post)

After months of campaigning, the "Leave" camp has won and Britain will be leaving the E.U. The Post's Adam Taylor talks about what that means for the country and Europe. (Adam Taylor,Jason Aldag/The Washington Post)

British voters have defied the will of their leaders, foreign allies and much of the political establishment by opting to rupture this country’s primary connection to Europe in a stunning result that will radiate economic and political uncertainty across the globe.

The voters’ decision to jettison Britain’s membership in the European Union was expected to jolt markets worldwide on Friday and unsettle Western capitals. By the time the BBC had called the result at dawn in London Friday, the pound had already plummeted to its lowest level against the dollar in decades.

The vote is perhaps the most dramatic to date in a wave of populist and nationalist uprisings occurring on both sides of the Atlantic that are overturning traditional notions of what is politically possible.

For months, the political and economic elite had looked on with growing apprehension as Britain flirted with a choice — popularly known as Brexit — that experts had warned could lead to global recession and a rip in the Western alliance. The vote could also lead to Scottish secession, a broader E.U. unraveling and the fall of Prime Minister David Cameron’s government.

But most analysts had predicted this pragmatically minded country would ultimately back away from the move, and opt to keep Britain in an organization regarded as a pillar of the global economic and political order.

British Prime Minister David Cameron announced that he will resign before negotiations begin to leave the European Union. "I will do everything I can in future to help this great country succeed," Cameron said. (Reuters)

Instead, a majority of British voters heeded the call of pro-Brexit campaigners to liberate the nation from what many here regard as an oppressive Brussels bureaucracy that enables mass migration into the country.

“Let June the 23rd go down in our history as our independence day!” cried a jubilant Nigel Farage, a firebrand anti-E.U. leader, in a 4 a.m. celebration. All around him, “leave” campaigners clinked pints of beer and cheered their improbable victory.

When polls closed six hours earlier, Farage had all but conceded defeat, saying he believed “remain” had won. But as results poured in through Thursday night and into the early hours of Friday, the “remain” camp was increasingly despairing.

About a third of results had yet to be counted as of 4 a.m. local time. But the BBC reported that “leave” had taken an insurmountable lead.

The results came after 15 hours of voting, from the remote Scottish isles to the tip of Gibraltar. The outcome revealed vast divides — with massive victory margins for “remain” in thriving metropolitan centers such as London and equally resounding victories for “leave” in small towns, rural areas and struggling, post-industrial cities.

[Three reasons that Americans should care about the British vote]

As local authorities announced results, markets swung wildly between optimism that the country would stay in, the preferred choice of investors, and pessimism that Britain had just voted to get out.

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After initially rising to a 2016 high, the pound plunged in international trading as jittery investors prepared for a scenario that had not been priced into market calculations.

As the hours ticked by, there was a dawning realization that Britain could become the first country to leave the 28-member E.U. In television interviews, “remain” supporters looked stricken and predicted catastrophe.

“God help our country,” tweeted Paddy Ashdown, the former Liberal Democrat leader and an outspoken E.U. advocate.

The outcome will rattle officials in Washington. President Obama had made a high-profile plea for Britain to stay. Presumptive Republican nominee Donald Trump, who was in Scotland on Friday to open a golf course, backed Brexit.

[If Britain leaves, who could be next?]

Although Britain may not actually leave the E.U. for years, Thursday’s vote fires the starting gun on what is widely expected to be a messy proceeding as Britain and E.U. officials begin untangling the vast web of connections between this island nation and the other 27 members of the bloc.

Thursday’s outcome will be a crippling blow to Cameron, who had campaigned vigorously for Britain to stay in the E.U. and had cast the referendum as a choice between an insular, intolerant “little England” and an outward-looking, pluralistic Great Britain.

Having failed to convince a majority of voters, he is expected to come under intense pressure to resign.

Cameron initially promised the referendum in 2013 in a bid to unite the country, and especially his Conservative Party, behind a common stance on an issue that has divided public opinion here for decades.

At the time, he may have expected a relatively easy victory. But the campaign soon went off script, as Justice Secretary Michael Gove and then-London Mayor Boris Johnson — friends and sparring partners of Cameron’s since his days at Oxford — both declared in February their intention to campaign for “out.”

The populist-minded Johnson will now be seen as the most likely successor to Cameron if the prime minister is pushed from his perch at 10 Downing Street.

“I think the Boris Johnson momentum will be unstoppable,” said Steven Fielding, a professor of political history at the University of Nottingham. “Cameron will try to find a dignified exit. But it’s not clear how long the backbenchers will give him to do that.”

The “leave” campaign found a compelling rallying cry with its call for voters to “Take Back Control,” a slogan that resonated among an electorate ill at ease with record levels of immigration — much of it from Europe under the E.U.’s free-movement policy.

Polls suggested that “leave” alienated some voters with its reliance on what critics saw as increasingly nativist rhetoric. That was particularly true after the killing last week of pro-E.U. lawmaker Jo Cox, a murder that appeared to awaken a passion in “remain” supporters that had been previously lacking.

A “leave” lead last week in the polls diminished, and the race turned into a dead heat. Surveys released Thursday as Britons votesdhad shown “remain” with a clear edge, results that cheered investors and boosted markets across Europe and Asia.

But as with last year’s British general election, the polls were badly wrong, apparently unable to capture the mood of an increasingly defiant electorate

The prevailing tone of the campaign on either side was fear and loathing, with neither venturing for long into hope or aspiration.

That spirit mirrored the angry mood of voters across the Atlantic, in the United States, and surprised even close observers of a nation that sees itself as deeply pragmatic and rational.

“Notions of Britain as a deferential, consensual society at ease with itself have been thrown out the window,” Fielding said. “This campaign has revealed a very profound mistrust among a substantial segment of society toward conventional political authority. The E.U. became a lightning rod for mistrust of politics more broadly.”

The vote split the country along essential lines: Old versus young. Provincial versus metropolitan. Scotland versus England. Native-born Britons versus immigrants.

[European press pens love notes to Britain]

As the first votes were cast nationwide — with the often-variable British weather running the gamut from a torrential downpour in London to sunny, clear skies in Scotland — anxiety was the prevailing mood.

Hilary Clarke, a 45-year-old stay-at-home mom, was the first to vote at a southwest London polling station. She said she would use her stubby pencil to check "remain" on her ballot.

“If I had been confident, I wouldn’t be standing in the rain at 7 in the morning,” she said as she sheltered beneath a colorful umbrella. "The reason I’m first in the queue is I’m going straight to the airport to go to Barcelona, and I may not return if vote goes the wrong way.”

Clarke said she could not understand the logic of those pushing for "leave."

"I can see that sometimes it seems we are hemorrhaging money to the E.U.," she said. "But at the same time, we seem to get so much more back than we give. Even if you’re disagreeing with what’s said at the table, it’s better to have a place at it."

But for "leave" voters, Britain's four decades of membership in the European Union and its precursors have only dragged the country down.

Andreas Hajialexandrou, a 48-year-old businessman of Greek Cypriot heritage, said the country could simply not withstand the impact of record numbers of immigrants from elsewhere in Europe.

“There are pressures on local services. I speak to our local [doctors] and they are just swamped,” he said. “The question is, how long can you support that level of immigration?”

Read more:

Would break from Brussels also splinter Britain? Probably not.

Why North America won’t copy European unity

The world marks Jo Cox’s birthday, days after British politician was slain

Today's coverage from Post correspondents around the world