The British Labour Party just split over Brexit and anti-Semitism. Here's everything you need to know.

Seven lawmakers from Britain’s opposition Labour party announced Monday they were quitting the party in protest at leader Jeremy Corbyn’s handling of an anti-Semitism scandal and Brexit.

The seven say they’re not forming a new party, but plan to sit together as the Independent Group in parliament.

“We have taken the step in leaving the old politics behind and invite others to do the same,” said Chuka Umunna, one of the defecting MPs, at a press conference in London, calling on other politicians from across the spectrum to join them.

Announcing their resignations alongside Umunna were MPs Luciana Berger, Gavin Shuker, Angela Smith, Chris Leslie, Mike Gapes, and Ann Coffey.

The defections, the biggest split within the party in decades, reflects strong dissatisfaction among some Labour MPs with leader Corbyn’s failure to effectively campaign to stop Brexit, and what they see as a lackluster response to allegations of anti-Semitism within the party.

Leader of the party since 2015, Corbyn rose to power with the backing of the grassroots, hard-left Momentum movement. While his unabashedly socialist politics saw the party pick up an extra 30 seats in the 2017 elections, he has alienated more moderate members, who feel he would make a disastrous prime minister.

“The Labour party that we joined that we campaigned for and believed in is no longer today’s Labour Party,” Leslie told reporters.

“We did everything we could to save it, but it has now been hijacked by the machine politics of the hard left.”

Although Britons voted by a narrow majority in 2016 to leave the European Union, many Leave voters say they have since changed their minds, claiming they were sold a misleading picture of the benefits of Brexit by the Vote Leave campaign.

Pro-Remainers have called publicly for a second, do-over referendum — the so-called “People’s Vote” — and have been disappointed by Corbyn’s failure, as leader of the opposition, to effectively campaign for such a vote.

Instead Corbyn — who was criticized for a barely-there campaign in support of Remain ahead of the referendum — has said Labour wants to keep the option of a second referendum “on the table” if the government is unable to reach a deal with the EU that can pass Parliament. However, he’d prefer another general election to a referendum.

His position has done nothing to break the messy deadlock over Brexit negotiations, or advance the cause of a second referendum — and has fueled speculation that he privately favors leaving the EU.

Leslie was scathing of Corbyn’s performance on Brexit, calling the issue “the tipping point” in his decision to leave. “Evidence of Labour’s betrayal on Europe is now visible for all to see. Offering to actually enable this government’s Brexit, constantly holding back from allowing the public a final say,” he said.

Another defecting MP, Gapes, said it was "increasingly clear that prominent figures in the Corbyn Labour leadership do not want to stop Brexit.”

The breakaway MPs also cited concerns with Corbyn’s response to an anti-Semitism scandal.

Berger, a Jewish MP who has faced anti-Semitic harassment from party supporters, said she was “embarrassed” and “ashamed” of the Labour Party, which she described as “institutionally anti-Semitic.”

Corbyn, who is known for his long-standing support for the Palestinian cause, has been accused of doing little to address concerns about anti-Semitic harassment within the party, despite publicly asserting his determination to stamp it out.

Gapes said he was leaving after being a member for 50 years as he was “sickened that the party is now a racist, anti-Semitic party and furious the Labour leadership is facilitating Brexit”.

He also felt that Corbyn would be a disastrous prime minister for Britain, as he had an anti-Western bias that put him “on the wrong side on so many international issues” — from Russia to Venezuela to Syria.

Although only seven MPs quit, many observers are speculating their departure could trigger a second wave of defections. A number of Labour MPs were reportedly very close to joining their colleagues Monday.

They could also be joined by disaffected pro-Remain MPs from the governing Conservative party — including those who have been involved in cross-party efforts with Umunna to push for a second EU referendum.

The defections could also consolidate the remaking of Labour in Corbyn’s image as a hard-left party, if Momentum activists within the party push to deselect moderates and centrists who share the defectors’ politics, in favor of their own candidates.

Momentum spokeswoman Laura Parker dismissed the defectors Monday as a “fringe minority” who wanted to return to the discredited politics of the Tony Blair-era. “With a back to the Blair years program of privatization, tax cuts for the rich and deregulation of the banks, they offer no concrete solutions, no new ideas, and have no support amongst the public,” she said.

READ: The man behind Brexit says there could be a do-over

Corbyn responded to the news by saying he was disappointed that the MPs “felt unable to continue to work together for the Labour policies that inspired millions at the last election,” while others in the party said those who quit should be made to contest by-elections to keep their remain MPs — something they’ve said they don’t intend to do.

High-ranking Labour MP John McDonnell warned that the split could thwart Labour’s chances at any future elections and effectively install the Conservative party in government for a decade.

Cover image: Labour MPs (left to right) Ann Coffey, Angela Smith, Chris Leslie, Chuka Umunna, Mike Gapes, Luciana Berger and Gavin Shuker after they announced their resignations during a press conference at County Hall in Westminster and the creation of a new Independent Group in the House of Commons. (Stefan Rousseau/PA Images via Getty Images)