LONDON — A day after British voters defied widespread warnings of economic and political peril should they cut ties with the European Union, the country reckoned with the consequences as markets tanked across the globe, the prime minister said he would resign and the United Kingdom felt the renewed pressure of a breakup.
The cascading developments, all within hours of the result of a deeply polarizing referendum, reflected a country shocked by its own decision.
The vote to leave the E.U. could mark one of the key turning points in modern British history, fundamentally reorienting the country’s place in the world.
But as of Friday, no one knew where Britain was headed, with joyous anti-E.U. voters celebrating “a glorious opportunity” and shattered Euro-philes warning of cataclysms to come.
At least in the short term, the pessimistic view appeared to be winning out Friday as the country endured layer upon layer of self-inflicted turmoil — and a sudden question over who would lead Britain at a crucial moment.
With Britain still absorbing the dawn news that the country had voted by a margin of 52 percent to 48 percent to withdraw from the E.U., an emotional Prime Minister David Cameron appeared in front of 10 Downing Street on Friday and said he would step down after championing a failed campaign.
He promised to remain as a caretaker through the summer but said he wanted Britain to have a new prime minister by early October.
“I will do everything I can as prime minister to steady the ship over the coming weeks and months,” he said with his wife, Samantha Cameron, standing at his side. “But I do not think it would be right for me to try to be the captain that steers our country to its next destination.”
Within hours, it became clear that whoever does the steering will have to fight to keep the United Kingdom from falling apart. Nicola Sturgeon, the leader in pro-E.U. Scotland, said she would push for a new independence referendum.
A 2014 vote failed, but Sturgeon said a rerun of that contest was “highly likely” in order to protect Scotland’s place in Europe after English and Welsh voters overrode Scottish objections and opted for “out.”
Nationalists in Northern Ireland — another area that favored remaining in the E.U. — echoed those calls, demanding a vote on Irish reunification.
As the political fallout emerged, plummeting markets made for a grim economic backdrop. The pound at one point fell to its lowest level against the dollar since 1985, before recovering modestly. Shares dropped from Tokyo to New York, with British markets hit particularly hard.
The market gyrations prompted Bank of England Governor Mark Carney to try to calm investors with a statement asserting that the bank was “well prepared” for the referendum’s outcome. The central bank, Carney said, was ready to intervene to prop up the economy.
In an extraordinary sign of Britain’s vulnerability as its vaunted currency plunged, the country’s fellow members in the Group of Seven club of wealthy nations issued a statement expressing confidence in the British economy — and vowing to take action to protect it.
Cameron also sought to reassure jittery markets, calling Britain’s economy “fundamentally sound” and saying there would be no immediate changes in the status of immigrants in the country.
The prime minister, in office since 2010, said he was stepping aside because the country deserved “fresh leadership” after he was unable to persuade a majority of voters to back his call to stay in Europe.
“The British people have voted to leave the European Union, and their will must be respected,” he said.
But Cameron said he would not immediately invoke Article 50 of the Lisbon Treaty, the never-before-used provision that allows E.U. members to leave the union.
The decision delays the start of divorce proceedings with Britain’s 27 E.U. partners. Cameron said that only after the transition in leadership would the country begin the formal process of withdrawing, which is supposed to take two years once it officially begins.
It was unclear, however, whether European leaders would allow Britain to wait. Top Brussels officials released a joint statement urging Britain to take the plunge into Brexit as soon as possible so as not to “unnecessarily prolong uncertainty.”
Cameron’s decision to step down set off an instant contest to replace him. Former London mayor Boris Johnson — a leading campaigner for the anti-E.U. cause — was considered the odds-on favorite.
Johnson was mobbed outside his house in north London early Friday, with some cheering but far more jeering a man whom many pro-E.U. Londoners blame for the outcome of Thursday’s referendum. “Shame on you!” some yelled.
In his first remarks after the vote, an uncharacteristically serious and even somber Johnson told reporters he was “sad” about Cameron’s resignation. He described the prime minister, a longtime friend and rival, as “one of the most extraordinary politicians of our age.”
The mop-haired Johnson did not say whether he would seek Cameron’s job. He did praise voters for rejecting the E.U., describing it as “a noble idea for its time” but one that “is no longer right for this country.”
“I believe we now have a glorious opportunity,” he said. “We can pass our laws and set our taxes entirely to the needs of the U.K. economy.”
Cameron’s successor will not be picked by the general public but instead in an internal process by his Conservative Party.
Since taking office in 2010, Cameron had sought to move the Tories toward the political center, championing gay marriage and taking a softer line on immigration than some in the party had sought.
But his repudiation in Thursday’s vote — fueled by an anti-immigration backlash — is likely to leave the party’s more hard-line anti-E.U. wing ascendant.
The domestic political backlash in Britain was not limited to the Tories: A pair of senior Labour Party members launched an attempt to oust their leader, the hard-left Jeremy Corbyn, following a lackluster Labour campaign to deliver an “in” vote.
Cameron’s pro-E.U. side had the backing of nearly every major world leader, including President Obama. In a statement Friday, the American president spoke of the deep U.S. bonds with Britain and the E.U. and said both would endure.
After speaking with Cameron and German Chancellor Angela Merkel, Obama later expressed confidence that Britain “is committed to an orderly transition out of the E.U.” The vote reflects “the ongoing changes and challenges that are raised by globalization,” he said at a conference at Stanford University.
“But while the U.K.’s relationship with the E.U. will change, one thing that will not change is the special relationship between our two nations,” Obama said. “That will endure. The E.U. will remain one of our indispensable partners. The NATO alliance will remain a cornerstone of our global security.”
Meanwhile, presumptive Republican presidential nominee Donald Trump, who was in Scotland on Friday to open a golf course, celebrated the Brexit vote and said he saw parallels with his own anti-establishment campaign.
“They took back their country,” said Trump, who sported a white “Make America Great Again” cap and was serenaded by bagpipers as he toured his course. “That’s a great thing.”
Iranian and Russian officials also cheered Britain’s vote, with a senior Iranian adviser to the country’s president tweeting that “the stars of the E.U.’s flag are falling down.”
Britain’s exit will indeed have a profound effect on the E.U., which will lose a major military and diplomatic power. “This looks to be a sad day for Europe and for Britain,” said Germany’s foreign minister, Frank-Walter Steinmeier.
Polls had forecast a narrow victory for “remain,” and most analysts concurred. But in the end, “leave” won by more than a million votes — out of some 33 million cast, representing nearly three-quarters of eligible voters.
The “remain” campaign won wide majorities in Scotland and London. The “leave” camp racked up resounding victories across provincial England, winning in small towns, rural areas and struggling postindustrial cities.
In a campaign marked by a relentlessly negative tone from both sides, “remain” was never able to answer charges from the “leave” campaign over immigration. Backed by the tabloid press, Brexit leaders portrayed the E.U. as an open door to millions of immigrants who threatened to change the country’s cultural fabric.
Instead of engaging on the issue, the “remain” camp changed the subject: It warned of the economic and political perils of departure — a line of attack that the pro-Brexit camp denounced as “Project Fear.”
But if Friday was an indication, the fear had real grounding.
Jeremy Greenstock, a retired senior British diplomat, wrote in an analysis that the impacts seen Friday were just the beginning and that Britain should brace for serious economic damage from job cuts, tax hikes, higher interest rates and reduced foreign investment.
Greenstock, now chairman of the Gatehouse Advisory firm, also warned that Britain would have less international clout for the foreseeable future.
Karla Adam in London and Brian Murphy in Washington contributed to this report.