Another group of anti-Corbyn MPs does not agree with either faction that forming a new party is the way forward. This view is said to be held by Luciana Berger, who appeared at the Independent Group event on Monday. “Luciana is not one of Leslie’s guys,” said a source. Berger told BuzzFeed News: "We are all in complete agreement".

Another major difference between rebel MPs is over whether they should fight by-elections after resigning the Labour whip. Some involved in the talks have argued that defeating a Labour candidate in a by-election fought over Brexit would give a new party a strong mandate and see them recognised as a major political force. Umunna, who has strong personal support in his Streatham constituency, which voted 79% Remain in the referendum, is seen as the most likely to succeed.

Other MPs have expressed vocal opposition to calling by-elections, fearing they would lose their seats. They want to instead stand in marginal constituencies at the next general election.

The MPs are also unclear on whether a new party should contest any upcoming by-elections in Peterborough and Newport West. Some believe it is important to run and set an early marker, but others fear that would mean turning both seats into Tory gains, spooking other rebels thinking about joining and making it easier for Labour to paint them as facilitating a Conservative government.

MPs considering leaving Labour have also disagreed on when is the best time to make their move. The party’s deputy leader Tom Watson is being credited from talking several anti-Corbyn MPs down from the ledge in recent days, asking them to delay their departures and make their case against the leadership from within. A Labour MP told BuzzFeed News: “Tom has been instrumental in keeping the numbers down and convincing MPs to stay”.

Some Labour MPs who did not resign today have privately committed to leaving the party and will stagger their announcements over the coming weeks, two sources said. These MPs felt that a “drip” of resignations would inflict maximum damage on Corbyn and that timing their departures for the next round of major Brexit votes on February 27 would be more effective, as it would clearly show the Labour leadership’s opposition to a second referendum.

Former leadership contender Owen Smith has already suggested he may quit the party over its Brexit stance and was notably quiet on Monday. Other names that have been floated include Ian Austin and Peter Kyle, although they both told BuzzFeed News they would not be leaving.

A senior Labour MP told BuzzFeed News: “I think more are already lined up to go, and haven’t gone today to try and give a sense of momentum over the next few weeks. I think some have deliberately been left behind on day one”.

Another Labour MP told BuzzFeed News that for some, their decision on whether they still have a place in Labour will depend on how the party deals with Monday’s breakaway. It “very much depends on how our leadership and their outriders behave,” they said.

However, there is similar uncertainty within the Tory Party. Anna Soubry, who is close to Umunna, is seen internally as the most likely to resign the Tory whip.