WOLVERHAMPTON, England — To understand the contradictions that are tearing the Labour Party apart, consider Ruth Wilkinson and Philip Handley, both Labour supporters. Ms. Wilkinson, 24, voted for Britain to remain in the European Union. Mr. Handley, 60, to leave.
The only bond that unites them is their fury at Jeremy Corbyn, the Labour leader, and his handling of the opposition to the government’s plan for Britain’s departure from the European Union, known as Brexit. And both are ready to ditch the party altogether.
“I’m absolutely devastated about the direction we’re traveling in,” Ms. Wilkinson, who works for a charity, said in an interview. “The party that I hold dear, and the party that I would stand behind, is not doing anything to offer a solution or an alternative.”
Mr. Handley said Labour had misled people like him.
“I’ve always voted for the Labour Party,” said the retired transport manager, who would prefer that Britain leave the bloc with no deal. “But this is the only thing I disagree with Jeremy Corbyn — how he handles Brexit.”
Eighteen months ago, Mr. Corbyn, 69, a longtime Labour outsider cast as a kind of far-left revolutionary, was riding a wave of popularity.
Labour had far exceeded modest expectations in a 2017 snap general election, and Mr. Corbyn had emerged as a surprisingly appealing figure, with young people memorably chanting his name at a music festival. He was seemingly primed to capitalize on the Conservatives’ infighting and missteps over the exit negotiations.
Instead, he is now openly at war with his own members of Parliament, nine of whom have defected in the space of two weeks. And the party is bleeding both Remain and Leave voters, while facing serious accusations of institutional anti-Semitism. There is talk of an existential threat.
Labour’s crisis is “much deeper than earlier crises,” said Mark Leonard, director of the European Council on Foreign Relations. “There is a standoff between the party and the country, the party and Parliament, and it’s difficult to see how you could cut your way through it.”
Brexit has proved to be politically lethal. Rather than pitting left against right, or the government against the opposition, it cuts across ideological lines, eating away at the cohesion of Britain’s largest parties, the Conservatives and Labour.
But Labour faces even broader forces.
In recent years, center-left, socialist-leaning parties across Europe have been fragmenting under an onslaught of right-wing populist parties catering to a broad swath of voters — older working classes and younger, urban people, loaded down with student debt.
Labour had seemed to be bucking that trend, but now is scrambling to avoid a devastating split.
Much of the blame, fairly or not, falls on Mr. Corbyn.
From the beginning of the Brexit debate, he has sought to lie low, content to criticize Prime Minister Theresa May while placating the main Labour constituencies — urban Remain voters and Leave supporters in rural areas or working communities, who make up about a third of the party’s electorate.
But as the Brexit deadline draws near, his efforts to appeal to both sides seem to be inflaming tensions rather than soothing them.
Labour is running the risk of “trying to compromise in several directions and antagonizing everyone,” said Robert Ford, professor of politics at the University of Manchester.
Even after suffering a string of setbacks and humiliations, Mrs. May is still seen as the more capable leader, and the Tories consistently outpoll Labour in opinion surveys. Mr. Corbyn, never popular with the majority of his own Labour lawmakers, has suffered a slump in his personal ratings.
The right-leaning Sunday Times recently claimed that 150,000 Labour members have already ditched the party over Mr. Corbyn’s position on Brexit, a number the party vigorously denies.
But there is no denying the defection of eight Labour members of Parliament, who left last month to form the Independent Group, citing Mr. Corbyn’s ambivalence over Brexit and his handling of anti-Semitism inside Labour. (Another lawmaker left, too, though that was because he supported Brexit and said he was disaffected by Mr. Corbyn’s leadership.)
“What we’re seeing now is that a series of deep divides, both recent and more longstanding, are coming out in the open, because a tipping point has been reached for many,” said Mr. Ford of the University of Manchester.
Mr. Corbyn moved quickly to staunch the rebellion, announcing that he would support a second referendum in the event of a “Tory Brexit.” But that seemed sure to anger Labour’s Remain voters.
Labour has always been divided between a moderate, internationalist, social democratic Left, and a radical, pacifist anti-imperialist Left.
“But the moderate side of the party has basically nearly always won,” Mr. Ford said. “Corbyn was the first time, probably since the 1930s, that the radical side of the party was in charge, and the rest of the party really doesn’t really like that, especially the members of Parliament.”
Mr. Corbyn himself embodies some of these contradictions: a lifelong Euroskeptic, he only grudgingly campaigned for Britain to remain in Europe during the 2016 referendum.
Since seizing the party leadership in 2015, Mr. Corbyn has enjoyed spurts of popularity, with party membership shooting up to an all-time high of more than 500,000 in 2016. But he was never able to win over the majority of Labour lawmakers, mostly moderates, who dismissed him as unelectable.
His success in the 2017 election shattered that notion, a point that paradoxically may be working against him now, analysts say.
“A lot of M.P.s in the party were basically expecting that he would go down to a crushing defeat,” said Mr. Ford, “and that then they would be able to regain control of the party, and this whole flirtation with the far-left would be some sort of horrible mistake and everyone would move on.”
So far, that has not happened, and Labour lawmakers are “starting to lose any reason to stick around,” he said.
Other tensions are playing out as well, especially between a pro-Corbyn grass roots movement and more socially conservative, working-class voters who believe Mr. Corbyn is too far to the left.
“He’s too Marxist for me,” said Stuart Williams, 73, a retired law lecturer, in Wolverhampton. Unable to abide the idea of voting for a Conservative, he plans to sit out the next election.
The stresses pulling Labour in opposite directions are equally reflected in the splintering of center-left parties across Europe in recent years, experts say.
In Germany, for example, the Alternative for Germany, a new far-right movement, is appealing to former industrial communities that the Social Democratic Party once owned. The Green Party is drawing young, urban voters away from the S.P.D., squeezing the Social Democrats from both sides.
In an effort to prevent even more M.P.s from defecting and to heal some of the divisions, Tom Watson, deputy Labour leader and a vocal critic of Mr. Corbyn, recently announced the creation of a moderate, social democratic group, the Future Britain Group, inside Labour.
“The departure of our colleagues is a real blow to us,” Mr. Watson recently told “The Andrew Marr Show,” “and we need to understand why they felt they need to go.”
But even impassioned Labour activists like Ms. Wilkinson are becoming disillusioned, long before Mr. Corbyn — or Labour — has a chance at making Downing Street his home.
“I haven’t seen them do anything effective in opposition at all,” Ms. Wilkinson said. “They are failing on Brexit, failing us on Brexit.”
“I’m angry at Corbyn,” she added.