With all districts declared, Prime Minister Boris Johnson’s Conservatives had won 365 seats — 48 more than they won in the last election, in 2017.
The victory is the party’s biggest since Margaret Thatcher captured a third term in 1987 — “literally before many of you were born,” Mr. Johnson told supporters Friday morning. It gives him a comfortable majority in the 650-seat House of Commons.
“We did it,” he said on Friday. “We smashed it, didn’t we?”
Jeremy Corbyn’s Labour Party had to reach even farther back to find a more extreme result. It won 203 seats, down 59 from the previous vote, in its worst showing since 1935. It had not suffered a similar drubbing since 1983, when it took 209 seats.
The Scottish National Party captured 48 of Scotland’s 59 seats, a gain of 13. The Liberal Democrats, who were hoping to ride an anti-Brexit stance back to prominence, won just 11 seats, one fewer than in 2017.
The Conservatives collected 43.6 percent of the popular vote, to 32.2 percent for Labour. That 11.3 percentage point margin was also the largest for the Tories since 1987 — a dramatic shift from 2017, when Labour lost the popular vote by just 2.4 percent.
Speaking to his constituents in Uxbridge early Friday morning, Prime Minister Boris Johnson said that the election results appeared to have given his government “a powerful new mandate to get Brexit done.”
Later in the morning, he told supporters, “we put an end to all those miserable threats of a second referendum” that might have reversed the results of the 2016 vote on Brexit.
“We will get Brexit done on time on the 31st of January — no ifs, no buts, no maybes,” he added.
He visited Buckingham Palace and met with Queen Elizabeth II, who formally asked him to form a new government.
He also promised that his government would spend more at home after a decade of austerity under Conservative governments — in particular on Britain’s National Health Service, known commonly as the N.H.S., a cherished program whose conditions have deteriorated.
Mr. Johnson said that he would seek “to unite this country and to take it forward and to focus on the priorities of the British people, and above all on the N.H.S.”
As hospital beds have overflowed, waiting times have gone up and vacancies have gone unfilled, many Britons have grown fearful that the health service could be privatized or otherwise overhauled — for instance by a trade deal with the United States that could drive up drug prices. (President Trump, tweeting congratulations on Friday morning, said Britain could “strike a massive new Trade Deal” after Brexit.)
Mr. Johnson insisted he would protect the health service, echoing his campaign promises to hire 50,000 more nurses and 6,000 doctors.
He promised again to hire more police officers, whose ranks have also thinned, and vowed “colossal new investments in infrastructure and science.”
“Let’s spread opportunity to every corner of the U.K.”
The Scottish National Party’s success — it won 48 of the 59 seats that it contested — will intensify the debate over independence for Scotland, which voted against Brexit and has largely rejected Britain’s major parties.
In a 2014 referendum, 45 percent of the voters in Scotland backed independence, and as Brexit approaches, the Scottish National Party, which backs independence, has insisted on a second referendum.
Mr. Johnson has said a national government under him would not hold a Scottish independence vote, but the Scottish government has suggested that it might go ahead with one. And on Friday morning, hours after the result of the vote was clear, Nicola Sturgeon, leader of the Scottish National Party and the first minister of Scotland, said it planned to do just that.
That raises the prospect of the kind of disarray and animosity plaguing Spain, where the government of Catalonia held an independence referendum two years ago that the central government said was illegal.
“It is clear beyond any doubt that the kind of future desired by the majority in Scotland is very different to that chosen by much of the rest of the U.K.,” Ms. Sturgeon told reporters during a news briefing.
“Scotland has rejected Boris Johnson and the Tories and yet again we have said no to Brexit,” Ms. Sturgeon said. She said within one week, the Scottish government would publish their plan for holding a new referendum.
“I accept, regretfully, that he has a mandate for Brexit in England,” she said. “But he has no mandate whatsoever to take Scotland out of the European Union.”
Ms. Sturgeon was clear that the decision on Scottish independence should be left up to the Scottish people, not the prime minister, to decide.
“The people of Scotland have spoken, it is time now to decide our own future,” she said.
Quim Torra, the separatist leader of Catalonia, congratulated Ms. Sturgeon on Twitter for “magnificent results that demonstrate the democratic will for independence.”
But politicians in Madrid have repeatedly rejected separatist attempts to compare Scotland and Catalonia, noting that Spain has a constitution that guarantees that national sovereignty resides with the whole Spanish people.
Speaking in his constituency of Islington in London, the Labour Party leader Jeremy Corbyn said that he would step down before the next general election, but would stay at the party’s helm for now, as it reflects on how to move forward from its dismal showing.
Mr. Corbyn is already under intense pressure to resign. His has been accused of poor leadership and of failing to handle accusations of anti-Semitism in the party ranks.
“I will not lead the party in any future general election campaign,” he said. “I will discuss with our party to ensure there is a process now of reflection on this result and on the policies that the party will take going forward and I will lead the party during that period to ensure that discussion takes place and we move on into the future.”
It was not clear how long Mr. Corbyn meant to stay on as party leader. The next election could be as long as five years away.
Some members of the Labour Party were quick to criticize him on Thursday night.
“The Labour Party has huge, huge questions to answer,” Ruth Smeeth, a former lawmaker, told Sky News. She immediately laid blame on Mr. Corbyn.
“Jeremy Corbyn should announce that he’s resigning as the leader of the Labour Party from his count today,” she said. “He should have gone many, many, many months ago.”
The pound jumped in value on Thursday night, buoyed by the receding prospect of a chaotic exit from the European Union without a divorce agreement. It began Friday near $1.35, up from about $1.32 a day earlier, but gave back most of that gain by late afternoon.
Equity markets were similarly lifted by the broad Conservative victory, with the FTSE 250 up more than 4 percent. The FTSE 100, which includes companies that rely more heavily on overseas earnings that would be dampened by a stronger pound, rose less sharply.
If the Conservatives manage to pass the withdrawal agreement bill as planned, the gains are likely to hold up through the end of the year, said Peter Dixon, an economist at Commerzbank. Easing global trade tensions should support markets too, after the United States and China, which have been locked in a trade war, settled on a partial deal.
Prospects look more uncertain for the new year.
The current deadline gives the British government has just 11 months to negotiate a complex deal on its long-term trading relationship with the European Union. The two sides may struggle to meet the Dec. 31, 2020 deadline, once again raising the prospect of a damaging “no-deal” Brexit.
“If negotiators get stuck or bogged down or become more fractious, there’s a prospect of more volatility in the currency,” Mr. Dixon said. “The risk of an accidental no-deal Brexit might keep the market on their toes.”
In the longer term, bond yields could also start to edge up if the Scottish secessionist movement gains momentum now that the Scottish National Party has won most of the seats in Scotland.
“The one thing which certain investors, maybe bond market investors, will look at again is the integrity of the U.K. following the strong Scottish result for the S.N.P.,” Mr. Dixon added.
European leaders on Friday welcomed the clarity of the British election result, which came during the last day of their summit meeting in Brussels, in hopes that it would make way for resolution of the Brexit deal.
Prime Minister Boris Johnson now has the majority needed to ratify his withdrawal agreement with Brussels by the Jan. 31 deadline laid out by Europe.
Charles Michel, president of the European Council, congratulated Mr. Johnson on Twitter and said that he expected British Parliament to vote on the deal “as soon as possible.”
But that will only start the clock on new negotiations about Britain’s future trading and security relationship with the bloc. Mr. Johnson has said that will be quick and easy, but few experts agree. It can be quick, Brussels argues, only if Britain agrees to keep its regulations and tariffs the very close to those of the European Union.
European leaders remain unsure whether Mr. Johnson, with a resounding mandate, will stick to his campaign pledge to finish any trade negotiation with the European Union by the end of 2020, or choose next summer to seek a year’s delay for longer talks. So long as they are negotiating, Britain is in a “transition” period, and its relationship with the European Union is essentially unchanged, even if it will be legally out of the bloc.
Xavier Bettel, Luxembourg’s prime minister, said he hoped that Mr. Johnson would deliver on his campaign promises, as “people need to have clarity.”
“I hope that with yesterday’s results, they do,” he said. “The excuse that there is no clear majority in London doesn’t last anymore.”
But talks on the future relationship between Britain and the European Union are “not going to be simple,’’ he said.
The Conservatives’ resounding win surprised many residents of Kensington, an area of West London that swung from Labour control for the last two years back to its longstanding Tory roots.
Most of them seemed to accept Boris Johnson as the lesser evil in an election that presented them with limited options.
“I was expecting a hung Parliament,” Brian Thompson, 71, said while walking Florence, a black Giant Schnauzer, just off Kensington High Street on Friday morning. Though not impressed with Mr. Johnson, he called the prime minister “the best out of a poor bunch.”
The race for the Kensington seat was one of the closest in the country, as it was in 2017, but the share of the vote going to the two main parties fell sharply.
Sebastian Gibson, 43, said he could not stomach either of them, and knew there would be no happy result for him. Mr. Gibson, a property buyer who voted in 2016 to remain in the European Union, voted on Thursday for the Liberal Democrats, who are anti-Brexit.
“It’s sad for the country,” he said of the election.
Mollie Lotery, 73, said she did not particularly like Mr. Johnson, but saw no real alternative.
“I don’t like Labour because I’m Jewish and he’s an anti-Semite,” she said of Mr. Corbyn. “I am delighted at the result.”
“We were excited to watch the election results, but this is bad,” said Mina Aden, 29, a community worker who is originally from Ethiopia. “We were expecting Labour would still have Kensington. The Conservatives have never done anything for human rights.”
Britain’s businesses welcomed the strong result for the Conservatives and the Brexit certainty it is expected to bring, at least for now. But they remain fearful of facing another Brexit deadline at the end of next year.
“The starting point must be rebuilding business confidence, and early reassurance on Brexit will be vital,” said Carolyn Fairbairn, the director general of the Confederation of British Industry, the country’s biggest business association.
Parts of the economy have been in limbo for much of the past three years, as negotiations with the European Union dragged on, and Parliament was unable to muster majority support for any one approach.
Both the Conservatives and Labour have worried the business community at different points. Labour had promised to nationalize some industries, while Boris Johnson had unnerved businesspeople with his determination to plow on with leaving the European Union, even without an agreement.
Now, companies want to know that they won’t be staring down another potentially disastrous deadline next year.
“Firms will continue to do all they can to prepare for Brexit, but will want to know they won’t face another no deal cliff-edge next year,” Ms. Fairbairn said.
And while the decisive victory paves the way for the next step in the Brexit process, one thing is clear: the postwar push toward greater global economic integration is at an end. The British election verdict is not the only sign.
In the United States, President Trump’s political base has rallied to his trade war against China. Popular movements across Europe have embraced nationalist and nativist causes that promise to halt globalization.
The traditional arbiter of trade disputes, the World Trade Organization, is listing toward irrelevance.
“The era of freewheeling markets and liberalism is ending,” said Meredith Crowley, an international trade expert at the University of Cambridge in England.
Britain will have a record number of female members of Parliament after Thursday’s vote, when women won at least 220 of the 650 seats, according to the Press Association.
At just over one-third of the House of Commons, women remain far short of parity with men, but they have made tremendous gains since the mid-1980s, when there were only 23 in Parliament. In the last general election, in 2017, women won 211 seats, a record at the time.
This year’s increase comes at a time when many people feared that women were being driven away from politics in a climate of heightened divisions. Online threats and abuse have risen sharply, and were disproportionately directed at female candidates.
Ahead of the campaign, more than a dozen prominent female lawmakers said they would not be standing for re-election citing that abuse as a reason for stepping away from politics. Many female candidates described threats and insults as a grim new reality on the campaign trail, a change that cast a harsh light on British politics.
An analysis of Twitter during the campaign, conducted by PoliMonitor, showed that all candidates received about four times as much abuse as in the 2017 election. The hostility aimed at women, the study said, was often based specifically on their sex or appearance.
Reporting was contributed by Richard Pérez-Peña, Megan Specia, Benjamin Mueller, Steven Erlanger, Ceylan Yeginsu, Amie Tsang, Stephen Castle, Elian Peltier, Peter S. Goodman, Raphael Minder, Iliana Magra and Alan Yuhas.