Video report from ITV News Political Correspondent Paul Brand
A group of seven Labour MPs have resigned from the party to sit in the House of Commons as independents, in the most significant split to hit the party since the breakaway of the Social Democratic Party in the early 1980s.
Luciana Berger, Chuka Umunna, Chris Leslie, Angela Smith, Mike Gapes, Gavin Shuker and Ann Coffey are among the MPs from the party's centrist wing who have been the loudest critics of Jeremy Corbyn's leadership, his stance on Brexit and his handling of allegations of anti-Semitism.
They issued an appeal to MPs from both Labour and other parties to "leave the old tribal politics behind" and join their new grouping.
The MPs have launched a new group called The Independent Group and their website launched on Monday morning.
At a press conference at London's County Hall to announce their move, Mr Umunna called on voters to display their support for the new Independent Group.
"For far too long, political parties in Westminster - parties of which we have been a part - have been failing you," he said.
"If you are sick and tired of politics as usual, guess what? So are we. That's why we have done what we have done today and why we commit to do things differently.
The Streatham MP added: "We don't have all the answers, so we will treat people like adults and be honest about the tough choices facing Britain.
He also ruled out the splinter group joining another political party.
"There are going to be no mergers - we are not going to join the Lib Dems, let's be absolutely clear about that," Mr Umunna said.
When asked by ITV News Political Correspondent Paul Brand if he would lead the party once it's ready, Mr Umunna said he would like to "play the biggest role" but added "it would be premature".
He said: "I want to play the biggest role that I can in any new movement, but given that we haven't even formed an organisation, and I've only just today resigned my membership from the Labour Party, I think it would be premature to start setting out my personal ambitions because it's not about me."
Ms Berger - who accidentally introduced herself as a "Labour Party MP", before correcting herself to "the Member of Parliament for Liverpool Wavertree" - said the decision to quit the party was "very difficult, painful, but necessary".
The MP, who has been the target of anti-Semitic abuse and was provided with personal protection at last year's party conference, said she had become "embarrassed and ashamed to remain in the Labour Party".
"I have not changed. The core values of equality for all, opportunity for all, anti-racism against all and social justice - the values which I hold really dear and which led me to join the Labour Party as a student almost 20 years ago - remain who I am," she said.
Mr Leslie - a former shadow chancellor - said Labour had been "hijacked by the machine politics of the hard left."
The MP for Nottingham East almost cries as he said: "I've been a Labour Party member for more than three decades but the Labour Party I joined is no longer today's Labour Party. I did everything I could to save it but it has now been hijacked by the machine politics of the hard left."
Mr Leslie added: "My values haven't changed. I absolutely oppose this Conservative government and desperately want an alternative which tackles the barriers of poverty and discrimination by extending opportunity for all.
"But British politics is now well and truly broken and in all conscience I cannot look you in the face and honestly urge you to support a Jeremy Corbyn-led Labour government."
There were 256 members in the Labour Party, however now there are 249, in comparison, there are 317 members in the Conservative Party.
Leader of the Labour Party, Jeremy Corbyn MP has said he is "disappointed" by the MPs' decision.
He said: "I am 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.
"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."
Labour MP Mary Creagh told ITV News she was "sad" to see seven Labour MPs resign before adding: "It is clear that Brexit is pushing both parties to breaking point."
The Wakefield MP added she was "immensely saddened" after hearing her "neighbour, colleague, and friend", Angela Smith, resign.
She also said Ms Smith had a "pretty horrible time" from her local Labour party, hinting that she had possibly been "bullied and intimidated".
Stockport MP Ms Coffey, who has represented Labour in the Commons since 1992, said the party was "no longer a broad church".
"Any criticism of the leadership is responded to with abuse and accusations of treachery," she said. "Anti-Semitism is rife and tolerated."
Mike Gapes, a former chairman of the Commons Foreign Affairs Committee, told the conference: "I am sickened that the Labour Party is now a racist, anti-Semitic party."
The MP for Ilford South said: "I am furious that the Labour leadership is complicit in facilitating Brexit, which will cause great economic, social and political damage to our country."
Mr Gapes added: "Jeremy Corbyn and those around him are on the wrong side on so many international issues - from Russia, to Syria, to Venezuela.
"A Corbyn Labour government would threaten our national security and international alliances."
Former Labour leader Ed Miliband tweeted: "I deeply regret the decision of my former colleagues to leave Labour. Labour's values are still my values and a Labour government is the best hope for the country we need.
"Labour must and will continue to be a broad church as it has always been."
Mayor of London Sadiq Khan has said he is "deeply distressed" by rumours of a Labour Party split, but admitted the party has been "shockingly poor" at dealing with anti-Semitism.
The Independent Group is due to hold its first formal meeting later this week, and released its first tweet just moments after being launched.
It said: "Today, seven MPs have left Labour and formed a new, Independent Group. They're from different backgrounds but are united in their belief that we can #ChangePolitics."