Corbyn’s office denied that he had anything to do with the list, which split Labour MPs into a series of categories, from a small band of “core supporters”, to those considered “hostile”.
Labour had been enjoying a brief respite from the internal conflict that has marked much of Corbyn’s tenure, as attention focused instead on last week’s budget, and the resignation of work and pensions secretary Iain Duncan Smith.
But the emergence of the list exposed the suspicion with which some on the right of the party are viewed, by some of Corbyn’s allies.
A spokesman for the Labour leader said: “It doesn’t come from this office and we have no knowledge of it.” He insisted that it did not represent the leader’s views.
Senior Labour insiders believe it may have emerged from a team of MPs loyal to Corbyn, calling themselves the “core”, who meet regularly – separately from the shadow cabinet – to discuss policy issues, and strategies for dealing with the divided state of the parliamentary party.
Among those identified as “hostile” in the list, were former shadow cabinet members Chuka Umunna, Chris Leslie and Rachel Reeves; leadership contender Liz Kendall; and even the party’s chief whip, Rosie Winterton – ostensibly responsible for ensuring loyalty to the leader.
John Woodcock, MP for Barrow in Furness, who was among this hostile group, said: “It’s sad that the public calls for unity and a new politics seems to be a front for this sort of internal attack operation, which harks back to the bad old days.”
He subsequently hastily withdrew a tweet he had accidentally published, referring to Corbyn as a “fucking disaster”.
Some members of the shadow cabinet, including shadow education secretary Lucy Powell, and shadow culture secretary Maria Eagle, were in another, only marginally more supportive group, badged, “core group negative”.
But others called for loyalty. Shadow culture secretary Gloria De Piero said, “Leaders office clear that list of Labour MPs is not from them. Must be someone with too much time on their hands. Suggest they campaign for the May elections”.
David Cameron made great play of the loyalty list in prime minister’s questions. He responded to a question from Labour MP Rushanara Ali about disability cuts by pointing out that it might win her promotion from the “neutral but not hostile” category.
At another point he yelled at Labour backbenchers, “hands up who’s ‘core support!’, saying that he and his government counted themselves in that category.
Jamie Reed, the MP for Copeland, told the website LabourList the issue had drawn attention away from the Conservatives’ travails over the budget. “We should be talking about the chaos and the civil war that is destabilising the Tory party,” he said.
Veteran Labour backbencher David Winnick, who was listed in the “core group plus” category, said he had never heard of anything like the list in his 59 years in parliament.
“If it came from the leader’s office, and I don’t see anywhere else it could have come from, I think it’s absolutely laughable,” he said, comparing it to the lists of “enemies” drawn up by US president Richard Nixon. He urged Corbyn and his team to “get a grip” on the situation.
There were multiple competing theories about how the leaked list emerged and who drew it up. One Labour MP suggested it was drawn up by a Corbyn loyalist in the whips’ office, rather than the leader’s office, and left in a House of Commons bar by mistake.
Others were convinced it was an attempt to mark out Labour MPs as targets for deselection by local activists ahead of the forthcoming boundary review.
As the list became the talk of Westminster, Iain Wright, Labour MP and chairman of the Commons business committee, tweeted: “Can’t move in the Tea Room for us Labour MPs asking each other: “where are you on the list?”
It also heightened speculation among MPs of a possible leadership challenge over the summer. Some Labour MPs are anxious about new figures they have been shown by a polling company that suggests the party has lost around a third of its support since May 2015.
Dan Jarvis, the former paratrooper widely touted as a potential future leader, was listed as “hostile”.
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