LONDON — Seven pro-Europe lawmakers abruptly quit the opposition Labour Party on Monday over their frustration with its leader Jeremy Corbyn’s handling of Brexit and anti-Semitism allegations in the ranks.

The seven said that they would sit in Parliament as an independent group. Their defection creates new opportunities and complications for the upcoming votes on how Britain leaves the European Union next month — if it leaves at all.

At a morning news conference, Parliament member Luciana Berger said she had become “embarrassed” and “ashamed” of the Labour Party, which she said was “institutionally anti-Semitic.” Berger, who is Jewish, added she was leaving behind a culture of “bullying, bigotry and intimidation.” 

Chris Leslie, another breakaway lawmaker, said the party had been “hijacked by the machine politics of the hard left” and that Labour’s “betrayal on Europe was visible for all to see.” While many Labour party members support a second referendum on whether to leave the European Union, Corbyn has been cold to the idea of a do-over.

Leslie said, however, that “our differences go far deeper than Brexit” — revealing the depth of antipathy to the 69-year-old Corbyn, whose self-described “radical” agenda for Britain energized new and young voters in the last election but has alienated the center of the party.

“The last three years have confirmed how irresponsible it would be to allow this leader of the opposition to take the office of prime minister of the United Kingdom. Many people still in the Labour Party will privately admit this to be true,” Leslie said.

“The pursuit of policies that would threaten our national security through hostility to NATO. The refusal to act when needed to help those when facing humanitarian distress, preferring to believe states hostile to our country rather than believing our police and security services — these are all rooted in the Labour leadership’s obsession with a narrow, outdated ideology,” Leslie said.

Corbyn said he was “disappointed” with the resignations but boasted of “the Labour policies that inspired millions at the last election and saw us increase our vote by the largest share since 1945.” Under the banner “for the many, not the few,” Labour votes surged in 2017, denying Prime Minister Theresa May a majority government.

Labour lawmakers said they were dismayed by the news of the resignations.

Lucy Powell, a member of Parliament, tweeted that it was the “wrong decision.” But she said that her friend and former colleague Berger had been subject to “despicable and appalling abuse.”

“Her leaving must make us redouble our efforts to tackle all antisemitism in the Party,” Powell tweeted. 

Corbyn has conceded that anti-Semitism is “a real problem that Labour is working to overcome.”

In a piece in the Guardian last year, Corbyn revealed that internal investigations of online chatter among party members found disturbing evidence that anti-Jewish “poison” was present. “Labour staff have seen examples of Holocaust denial, crude stereotypes of Jewish bankers, conspiracy theories blaming 9/11 on Israel, and even one individual who appeared to believe that Hitler had been misunderstood,” Corbyn wrote.

London Mayor Sadiq Khan, a star in the Labour Party, said he wished the departing members would have stayed: “This is a desperately sad day. These seven MPs are all friends of mine.”

Writing on his Facebook page, Khan agreed that there needed to be another Brexit referendum and that Labour needed to do more to “root out the evil of anti-Semitism.”

But he argued it should be done from within the party. 

“When the Labour Party splits it only leads to one outcome — a Tory government — and that means a hard Tory Brexit,” he wrote.

The defection of a small number of lawmakers can dramatically change the political math, especially now, when Labour and the governing Conservative Party are both bitterly divided over the way forward on Brexit.

In 2014, two Conservative lawmakers defected to the U.K. Independence Party, which rattled the Tories and contributed to then-Prime Minister David Cameron’s decision to call for the Brexit referendum and settle the matter once and for all in his own party.

The Labour resignations on Monday were being compared to the rupture in 1981 — until now, the biggest split in Labour — that saw four heavy-hitting Labour lawmakers break away to form the Social Democratic Party.

Vince Cable, leader of the Liberal Democrats, a small center-left party, told the BBC he was keen to work with the new group, which he speculated could grow in coming days. 

“We shouldn’t forget the Conservatives are also very badly split and there are quite a few of them who no longer see a future in the Conservative Party,” Cable said. “So I think this is the beginning, rather than the end, of something rather important.”