In a press conference on Monday, the MPs – who also include Gavin Shuker, Angela Smith, Chris Leslie, Mike Gapes and Ann Coffey – said Corbyn’s Labour had radically departed from their values.
Their departure is the biggest split in Labour since the “gang of four” senior figures left the party in 1981 to form the Social Democratic party (SDP).
Umunna said they were taking the first step to forming a new movement, as he called on politicians from other parties to join them.
The former shadow cabinet minister said the established parties “cannot be the change because they have become the problem”, and put party interests above the national interest. He said it was “time we dumped this country’s old-fashioned politics” and created an alternative.
Berger, the MP for Liverpool Wavertree, said it had been a “difficult, painful but necessary decision” for them all, before criticising Labour for becoming “sickeningly institutionally racist”.
The Jewish MP, who is heavily pregnant and has been subject to antisemitic abuse, said she had become “embarrassed and ashamed” to be in the Labour party because of its failure to tackle antisemitism in its ranks.
“I am leaving behind a culture of bullying, bigotry and intimidation. I look forward to a future serving with colleagues who respect each other,” she said.
Leslie, the MP for Nottingham East and a former shadow chancellor, said Labour had been “hijacked by the machine politics of the hard left” and was no longer the party he and others had joined.
Gapes said he was “sickened that Labour is now a racist party” and he believed its leader was “on the wrong side on so many international issues” from Russia to Syria.
In response, Corbyn said he was “disappointed that these MPs have felt unable to continue to work together for the Labour policies that inspired millions at the last election and saw us increase our vote by the largest share since 1945”.
“Labour won people over on a programme for the many not the few – redistributing wealth and power, taking vital resources into public ownership, investing in every region and nation, and tackling climate change,” he added.
“The Conservative government is bungling Brexit, while Labour has set out a unifying and credible alternative plan. When millions are facing the misery of universal credit, rising crime, homelessness and poverty, now more than ever is the time to bring people together to build a better future for us all.”
There has been speculation that several centrist Conservative politicianswere also considering their future in the party over Theresa May’s EU policy. Umunna has worked closely with Anna Soubry, the MP for Broxtowe, Heidi Allen, the MP for South Cambridgeshire, and Sarah Wollaston, the MP for Totnes, on a second referendum.
MPs from both parties have been facing the threat of possible deselections where their views clash with local constituency members either over Brexit or their loyalty to the leadership.
The announcement will be met with dismay and fury in other parts of the Labour party, after colleagues spent weeks trying to persuade them to stay.
John McDonnell, the shadow chancellor, warned on Sunday that MPs quitting could cause a decade of Tory rule, as it risked splitting the Labour vote in their constituencies.
“It would be like the 1980s. In my constituency in Hayes and Harlington we had a Labour MP join the SDP and we lost the seat to the Conservatives,” he told the BBC’s The Andrew Marr Show.
“And it basically installed Mrs Thatcher in power for that decade. I don’t think any of the people who have even been mentioned around this split would want that.”
Michael Dugher, a former MP, aide to Gordon Brown and senior figure in Ed Miliband’s shadow team, quit Labour this weekend claiming the party he joined nearly three decades ago “no longer exists” and argued it was “institutionally antisemitic”.
Some in Labour have appeared to be goading the grouping to split. Last week, Momentum released a spoof Valentine’s Day video aimed at Umunna, set to the song Please Don’t Go. It urged him to stay in the party, but concluded: “If you go we’re keeping the house xxx.”