Jane Onyanga-Omara, and Kim Hjelmgaard

USA TODAY

LONDON — The United Kingdom voted to leave the European Union, according to a BBC forecast based on a partial count of results Friday.

The margin of victory was 52% to 48%.

It is the first departure from the alliance since the EU was formed 43 years ago. It could prompt other member nations to follow the U.K.'s lead and reverse a decades-long drive for European unity.

The outcome sent global markets into a tailspin. It will have far-reaching political implications for the future of the 28-nation bloc as well as the political future of Prime Minister David Cameron.

Nigel Farage, leader of the U.K. Independence Party said that "dawn was breaking on an independent U.K." He is not an member of the official "leave" campaign, but supports an exit from the EU.

The British pound fell 11% to a 31-year low as the "leave" camp appeared on course to win the historic referendum. Dow futures plummeted more than 600 points. Tokyo's Nikkei index fell 8%. London's FTSE index was due to open 7% lower amid a flight to safety.

Iain Murray, vice president for strategy at the Competitive Enterprise Institute, a Washington-based public policy organization, said Britain’s "surprising vote" to leave the EU is "only the start of uncertainty and opportunity."

"Negotiations over the terms of exit will take at least two years, and no one knows what form they will take or what deal can be struck,” he said.

The British currency initially soared to a 2016 peak of $1.50 amid signs that "remain" was winning the day, but then moved lower with losses accelerating. It fell from $1.50 to below $1.35 as results suggested a strong possibility the U.K. would vote to quit the bloc

The final poll from online research firm YouGov had “remain” on 52% and “leave” on 48%. While not an exit poll, the survey was conducted on the day of the referendum.

The four-month campaign has been acrimonious. Backers argued that severing ties with the EU is the only way to reduce a flood of migrants and protect the U.K.'s independence from burdensome EU regulation.

Supporters of remaining in the EU, led by Prime Minister David Cameron, said jobs, the economy, national security and the U.K.'s standing on the world stage would be compromised outside the alliance.

The Electoral Commission said a record 46.5 million people registered to vote. The question on the ballot paper was: "Should the United Kingdom remain a member of the European Union or leave the European Union?" The side that gets more than 50% of the votes will win.

The tiny overseas British territory Gibraltar was the first counting area to report results. The 2.5 square mile area off the south coast of Spain backed "remain" by a vote of 19,322 to 823 — an overwhelming 95.8%. A count by the Electoral Commission is underway across 381 other counting areas. Gibraltar had been expected to strongly favor “remain.”

In Rome, Italy's finance minister, Pier Carlo Padoan, was quoted as saying at a forum Thursday that no matter what happens, it will be impossible to assert "let's pick up as if nothing" happened.

It is the U.K.'s third nationwide referendum, and its second on EU membership. U.K. voters backed staying in the EU in 1975. Scotland failed to win independence in a 2014 vote that was held only north of the border.

Eligible voters included British, Irish and Commonwealth citizens over 18 who are residents in the U.K., that is, England, Scotland, Wales and Northern Ireland. Also voting were U.K. nationals living abroad who have been registered voters in the U.K. in the past 15 years. In addition, members of the House of Lords and commonwealth citizens in Gibraltar were also able to vote, unlike in a general election.

Voting was disrupted in the South of England Thursday as flash floods forced some polling stations to be relocated.

Peter Carlyon, 22, who was campaigning to stay in the EU in central London on Thursday, said the vote was "a once in a generation" chance. "We can’t change our minds next week.”

But Kevin Campbell, 36, said that an influx of Eastern Europeans coming to the U.K. under the EU's freedom of movement laws was damaging his small business. He works for a firm that installs fire-protection systems.

When will we know the result of the 'Brexit' vote?

Cameron issued a referendum day plea on Twitter for Britons to vote to “remain” while his Conservative Party rival Boris Johnson urged the country to “leave.”

Later Thursday, Johnson unveiled a poster that said “last chance to vote" at his daughter Lara's graduation ceremony at St. Andrews University in Scotland, according to media reports.

While many observers feel Cameron will have to resign if Britons vote to leave the EU bloc, dozens of Conservative "leave" lawmakers have signed a letter saying the prime minister should stay in office whichever side wins the membership referendum.

The letter signed by 84 legislators says “whatever the British people, decide you have both a mandate and a duty to continue leading the nation implementing our policies.”

That leaves more than 60 Brexit-supporting Conservative Party lawmakers who did not sign.