Sir Keir Starmer has been dragged into a bitter bullying row by his own Labour members as his allies on Saturday accused supporters of Rebecca Long-Bailey of orchestrating another “smear” against him.

The Sunday Telegraph can reveal that the frontrunner to become Labour’s next leader has been accused of standing by while “right-wing” members in his local constituency party subjected Corbynistas to “hostility and abuse”.

The “chronic factionalism” has now spilled out into the open, with 31 members of his Holborn and St Pancras branch writing to Labour’s general secretary Jennie Formby to demand she intervene.

In their letter, obtained by this newspaper, the members allege that while Sir Keir has made unifying Labour’s warring factions one of his key leadership priorities, “he has not tried to foster unity within our CLP [Constituency Labour Party].”

Urging Ms Formby to step in, they claim that “socialist members” have been “marginalised and made to feel unwelcome”, adding that they have “grave concerns” that if Sir Keir is elected “all socialists in the party will be treated as we have been.”

Hitting back on Sunday, an ally of Sir Keir dismissed the allegations as a “desperate and naked attack” from the “far-Left” at “crucial stage in the election campaign”.

“One thing that all of us know about Keir is that he plays by the book and is committed to justice and fair play,” they added. “The campaign that is being run against him really is in the gutter at this stage.”

A second source claimed they did "not recognise the content of the comments", adding that Sir Keir was "proud to have been overwhelmingly reselected by his local party last year."