LONDON — Jeremy Corbyn strengthened his grip on Britain's opposition Labour Party on Saturday, beating back a challenge to his leadership by members of Parliament with increased support from the party's rank and file.
The results of the summer-long leadership struggle were announced in Liverpool, in northwestern England, on the eve of the annual Labour Party conference.
Corbyn, a 67-year-old hard-left politician, won 61.8 percent of the more than 500,000 votes cast, up from the 59.5 percent he received a year ago, when his victory shocked and divided the party.
A revolt by Labour members of Parliament, who said they feared that Corbyn would lead the party to electoral disaster, came to nothing as their favored candidate, Owen Smith, won only 38.2 percent of the vote.
The result tightened Corbyn's grip on the party and isolated many of its members of Parliament from a growing membership that is younger and more left-leaning, drawn by Corbyn's policies to reduce inequality, make Britain nonnuclear, and renationalize key areas of the economy, like the railways and energy.
The party has almost tripled its membership to more than 500,000, making it the largest in Western Europe, Corbyn said. But opinion polls regularly indicate that if an election were held tomorrow, Labour under Corbyn would suffer a historic defeat in the country as a whole.
In a victory speech, Corbyn called for unity, said more held "the Labour family" together than divided it, and vowed that the party would win the next election under his leadership.
Corbyn also promised forgiveness to the rebels, noting that many heated things are said in a campaign that are later regretted. "Let's wipe that slate clean from today and get on with the work we have to do as a party together," he said.
There are concerns among the rebels in Parliament that Corbyn and his team will move against them. Electoral districts are to undergo boundary changes as the House of Commons shrinks from 650 members to 600, and Corbyn's opponents fear the leadership team will use those changes to replace them with other candidates. Some of Corbyn's allies have been pressing for "mandatory reselection" of all candidates in every district before another British election.
Anticipating his victory before it was announced, Corbyn had issued a plea for unity. "Whatever the result, whatever the margin, we all have a duty to unite, cherish, and build our movement," he said.
Corbyn and his allies see Labour as a socialist movement whose purpose is to change society. But most Labour members of Parliament, who regard Corbyn as a man of the old-fashioned, hard-left fringe, believe the best way to effect change is to win power in elections, which in Britain has meant moving toward the center, not farther to the left.
They have also criticized Corbyn for poor organization and weak leadership, and have said Labour is not doing its job as an effective opposition to the governing Conservative Party.
But after this resounding victory, Corbyn is highly unlikely to face another challenge before the next general election, due in May 2020. Labour members of Parliament who refused to serve in his shadow Cabinet, or who resigned from it as part of the revolt, will be under pressure to join it, even if they sharply disagree with his policies.
Tony Travers, a professor of government at the London School of Economics, said the Labour Party was "like a miserable, unhappy family trying to coexist."
Labour's home affairs spokesman, Andy Burnham, told BBC radio that while the party's "war of attrition" must stop, Corbyn must also build more support among the general public, not just among Labour activists.
"No one gets the right to take Labour down to a devastating defeat," said Burnham, who is trying to avoid the party's parliamentary problems by running for mayor of Manchester.
Some Conservatives have urged the new British prime minister, Theresa May, who took over from David Cameron, to change the law to call an election sooner, in order to get her own mandate and take advantage of the divisions in Labour. But she has said there will be no early election.
David Miliband, former Labour foreign secretary and a centrist narrowly beaten to the party leadership in 2010 by his more left-leaning brother, Ed, wrote in the New Statesman magazine this past week: "We have not been further from power since the 1930s."