One of Westminster’s most dramatic days since the Brexit referendum began in silence. One-by-one, seven Labour MPs looked across a table at one another and pressed send on emails destined to make history.

Their bombshell “statement of independence” informed Jeremy Corbyn, the party’s most left-wing leader since the 1980s, they were resigning to sit as The Independent Group (TIG).  

“There were no doubters,” Luciana Berger, the MP for Liverpool Wavertree, told HuffPost UK at the end of a day that is likely to reverberate for months.

Berger added it was the alleged refusal of her former party to deal with anti-Semitism that drove her to leave.

“It would have been much easier for me to put my head in the sand and my fingers in my ears but this is about every organ of the party, from the NEC, the general secretary to Jeremy himself and the shadow cabinet. There doesn’t seem to be any desire to contend with the issue of anti-Semitism, and I couldn’t see that changing,” she said.

Moments later, she, Chuka Umunna, Chris Leslie, Angela Smith, Mike Gapes, Ann Coffey and Gavin Shuker filed into the next room, overlooking a choppy River Thames and Westminster Bridge, to explain their joint decision to a crowd of journalists.

Berger said her party had become “institutionally anti-Semitic”, while others cited deep frustration with Corbyn’s Brexit policy as the driver of the ‘gang of seven’ and its shock move. 

“Politics is broken, it doesn’t have to be this way, let’s change it,” Umunna told the press conference.

“If you are sick and tired of politics as usual, guess what? So are we,” added the Streatham MP, whose name has long been associated with whispers of a breakaway.

Whether the new parliamentary caucus triggers an En Marche-style centrist party, which swept Emmanuel Macron to power in France, remains to be seen. But as the news sunk in for the rank and file, statements declaring sadness and heartache quickly descended into briefing and counter-briefing.

Questions immediately began to swirl over how TIG will be funded as a new website and accompanying crowdfunder page crashed due to a rush of interest. Key figures refused to name any large donor. “If you want to build something new, if you feel as politically homeless as us, this is the moment to build it,” said Shuker when pressed. 

While facing instant criticism from Corbyn loyalists, TIG’s first major error was entirely self-inflicted. Smith became embroiled in a racism row barely two hours after the new group was formed when she described BAME voters as having a “funny tinge” in a BBC interview. She later apologised. 

And in a sign of the full-on warfare set to grip the party, Ealing Labour MP Rupa Huq, in a statement sent from Corbyn’s office, said the group should immediately investigate the “appalling, racist comment”. 

As the day wore on, the true ramifications of the Labour split started to emerge. 

Tom Watson, the party’s deputy leader and a key figure on the moderate wing, urged left-wingers to shelve their anger and instead reach out. He demanded Corbyn make good on his tagline pledge to create a “kinder, gentler politics” and embark on a shadow cabinet reshuffle.

“The tragedy of the hard left is that they can be too easily tempted into the language of heresy and treachery,” he said, before making clear he does not regard those who quit as “traitors”. 

As anger over anti-Semitism reverberated around the Parliamentary Labour Party (PLP) over Berger’s exit, Watson attempted to curb further losses, adding: “They say anti-Semitism is a light sleeper. This is certainly a wake up call for the Labour Party.”

Other MPs would be “asking themselves how they can stay”, he admitted, before appealing for Labour to return to its “social democratic” and “mainstream” traditions. 

“I love this party. But sometimes I no longer recognise it,” he said. 

While some remained hopeful Berger would return, it was clear there was no route back for some of the other breakers.

In one stunning moment, Leslie, asked by Sky News’ Kay Burley on whether he saw Labour as “rotten to the core”, replied simply: “Yes I do.”  

Party chair Ian Lavery, who once said Labour was “too broad a church”, later addressed the weekly meeting of the PLP, making an emotional plea for MPs to remember the party’s key achievements, such as the NHS and Sure Start children’s centres. 

But anger over the party’s apparent failure to tackle anti-Semitism became the flash point. “That was a meeting of two halves,” one MP said as he left.  One MP described it as “a dialogue of the deaf” while another walked out in disgust, muttering “absolute rubbish”.

Walthamstow’s Stella Creasy could be heard telling the meeting there could be “no more” of what she called “constructive dismissals” of MPs such as Berger over anti-Semitism. 

Speaking after the tumultuous meeting, Dudley North MP Ian Austin said others were considering whether to join TIG. “If that is the best the leadership can do then people will be thinking long and hard about their position in the Labour Party,” he said, citing anti-Semitism as the main cause for the breakaway. 

Jewish Labour MPs Ruth Smeeth and Louise Ellman were said to have raised the case of a member who allegedly said the pair “did not have human blood”. “(Smeeth) raised it months and months ago and the person is still a member of the party and has not yet been suspended,” said Austin.  

He called Shadow Chancellor John McDonnell’s demand that Berger should have pledged loyalty to the Labour Party to escape a local motion of no-confidence as “like something out of Stalinist Russia”. “I think constructive dismissal is a pretty good way of summing this up,” he added. 

McDonnell was seen entering the meeting, as was the party’s shadow justice secretary Richard Burgon, another Corbyn loyalist, but did not speak, despite the enormity of the day’s events, Austin said. Corbyn was not at the meeting and was said to have been at a funeral.

The growing influence of the Unite union and Len McCluskey was one reason behind the breakaway, HuffPost UK understands. Its relationship with Labour has become “dysfunctional”, one TIG source said.

The Unite boss recently signalled remaining in the EU should be off the table and that a second referendum threatened democracy. Labour Leave organiser Brendan Chilton, who has been lobbying Labour MPs to push through Brexit, told HuffPost UK he “absolutely” regarded McCluskey as an ally, adding: “He has made some very powerful interventions.”

One of the most vicious responses to the septet’s move was also from the Unite boss himself. He told the BBC there was a “strong whiff of hypocrisy” about the resignations and that the “splitters” had “no stomach for a fight” on Labour’s radical new policy agenda. “History will judge them,” he said. 

Tim Roache, general secretary of the GMB union, tried to strike a different tone and encourage wavering MPs to stay. “I gritted my teeth through the Blair era, when I disagreed with the Labour government on a host of issues. But I stayed in the party because Labour in power is always better than the alternative,” he said. 

Meanwhile, as Labour backbenchers demand the leadership see through pledges to campaign for a second referendum, shadow cabinet members tried to stem further resignations, cautioning it would not force Corbyn to switch policy. 

On Facebook, Emily Thornberry, viewed as a successor to Corbyn, conceded the exits could damage Labour’s electoral prospects in Conservative marginals, adding they could “make a Tory Brexit more likely, not less”.

She also appealed for calm, telling members: “If you criticise or abuse these individuals, if you impugn their motives, and if you encourage any others to join them, you are helping them not hurting them, because you are taking your eyes off the prize and allowing our movement to be distracted and divided, which is exactly what they want.” 

Burgon was more hardline, calling the move a “direct attack on the Labour Party”. “They also risk doing more damage to the call for a second referendum than to the Labour Party, which is why so many have been so quick to distance themselves from Chuka’s coalition today,” he said.

But will the grouping be joined by Tory Remainers rather than more MPs from the Labour side (Berger admitted she had received messages of support “from all sides of the house”)? Pro-Remain Tories, such as Sarah Wollaston and Nick Boles, may be tempted to join TIG against a backdrop of tensions with the hardline Brexiteer group, the ERG. However, party chairman Brandon Lewis released a short statement taking aim at Corbyn.

Fuelling more speculation over the formation of a party of many stripes, former chancellor turned Evening Standard editor George Osborne, a critic of May’s pro-Brexit direction, raised eyebrows when he later tweeted it “could be the start of something very big in British politics”. 

Smith, meanwhile, rejected comparisons with the Social Democratic Party (SDP) breakaway in 1981. “I just don’t think the comparison with the SDP stands up to scrutiny,” said claimed. “This is a different century and the challenges that the country faces are on a scale that I don’t think we have seen at any other time in the post-war period.”

Umunna ruled out the splinter group joining another political party. He said: “There are going to be no mergers – we are not going to join the Lib Dems, let’s be absolutely clear about that. If there are other MPs who share our values we’re offering, then join our movement.” 

To cap a tumultuous day, the rift between Labour’s moderates and left-wingers threatened to get deeper still as reports emerged that Derek Hatton – a ringleader of the notorious Trotskyist Militant group, banned from the party by Neil Kinnock in the 1980s – had rejoined the party.  

Hatton, whose case Labour would not comment on, said the breakaway MPs were “very, very selfish, very, very hypocritical”. And, in comments likely to provoke fury from some, he told Buzzfeed: “As far as I’m concerned now they should all resign and call by-elections.”