It started as a fringe demand and grew into a mass movement. Now leading advocates of a People’s Vote — or a second Brexit referendum — are admitting that they are unlikely to succeed this side of a general election.

Liberal Democrat MP Chuka Umunna told Sky’s Sophy Ridge show on Sunday that “it simply does not look like” the numbers are there for a second referendum.

Just two weeks ago, his party was adamant that it is a referendum, not an early election, that could solve Brexit. “Boris Johnson is determined to have a general election,” Lib Dem leader Jo Swinson said then, “but the best way to resolve the Brexit chaos is to have a people’s vote.”

Now Swinson has joined forces with the Scottish National Party to push for a December 9 poll instead. “If the Labour Party had wholeheartedly come on board with the People’s Vote campaign, we might have been able to deliver that at an earlier stage,” she told BBC Radio 4’s "Today" program.

It is a public acknowledgement of a reality that has been clear for months. Each time it has been put to a vote in parliament, a second referendum proposal has been defeated. The closest it came to passing was in April, when it was rejected by 12 votes — and then only in a non-binding, indicative vote with numerous abstentions.

The likelihood of a second referendum now looks dimmer still after divisions inside the People’s Vote campaign group reached boiling point last night.

The likelihood of a second referendum now looks dimmer still after divisions inside the People’s Vote campaign group reached boiling point last night. Two of its leading figures — director James McGrory, and head of comms Tom Baldwin — were unexpectedly fired in an email from Roland Rudd, the chairman of Open Britain, one of the organizations that makes up the campaign.

Senior campaign figures were locked in a broadcasting war this morning, with Baldwin telling the Today program that he won’t accept his dismissal by Rudd. “I don’t work for Roland Rudd,” he said, adding that “it doesn’t seem to be the best week for putting a wrecking ball through the campaign.”

The mood in People’s Vote HQ was sour this morning, and one official said Rudd had canceled a morning meeting where he was due to face questions. “The People’s Vote campaign belongs to the people who work on it and the campaigners and activists who give their time to it and the people who show up to campaign for it. It does not belong to Roland Rudd,” they said.

One staffer — an ally of Rudd — said the boss pulled out of the meeting this morning after workers tried to “ambush” him and film him. A third of the workforce stormed out of the office and ended up with a day off. The staff member said the dispute was triggered three months ago when People’s Vote bigwigs Alastair Campbell and Peter Mandelson tried to oust Rudd from his position.

“James and Tom are not going to come back. Clearly they have been dismissed they are former staff,” they added. “It’s a distraction that we could have done without. But there is never a good time for these things — especially in Brexit. Every day is a crisis.”

Labour, too, has twisted the knife, with Shadow Chancellor John McDonnell tweeting that the Lib Dems and SNP had “given up” on a referendum. Peter Kyle, one of the architects of the proposal to put any Brexit deal to a confirmatory vote, tweeted: “A million people have twice marched in support of a final say referendum. No one has marched for a general election.”

But with both the Lib Dems and the SNP now backing an election before a people’s vote — and willing to force a vote on the issue in parliament Tuesday — the growing likelihood is that it will be up to a new parliament to decide.

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This article has been updated to correct the spelling of Alastair Campbell's name.