Keir Starmer has warned Labour Party members they will lose the next general election if they do not abandon the “factionalism” of recent years.

The new Labour leader’s first days in office have been hit by an explosive internal party row over a leaked dossier that detailed bitter ideological and personal splits between the so-called right and left of the party.

The report, seen by HuffPost UK, claimed Labour’s HQ in Westminster had been consumed by a “hyper-factional atmosphere” in which, for some staff opposed to Jeremy Corbyn’s leadership, “the worse things got for Labour the happier they would be”.

In a Zoom video call with party members on Wednesday evening, Starmer, who took over from Corbyn on April 4, made a plea for unity.

“We have to stop the factionalism in our party. We have to create a different culture where we respect and support each other in a different way,” he said.

“We are going to have to have change here. We have got to bury this factionalism that has meant too many people seeing things through factional eyes instead of pulling tougher and supporting our party.

“If we carry on taking lumps out of each other we are heading for a loss at the next general election.

“If we lose the next general election, that will be five in a row, and we will be out of power as a party for longer than any period since the Second World War.”

Starmer warned that “everybody who is taking a lump out of somebody else” in the party was “letting down” the voters “that most need us”.

The Labour leader added he and deputy leader Angela Rayner would always present a “united” front.

“There won’t be any splits or differences between us,” he pledged. 

Rayner, who hosted the call with party members from the flat she shares with former party leadership candidate Rebecca Long-Bailey, said she recognised the contents of the report had “upset” many party members.

Starmer and Rayner have commissioned an independent inquiry into the contents of the document as well as how it was leaked.

Rayner told party members it would not be “pushed into long grass” and would deliver a “swift response”.

“We do not believe that this is something that should go away,” Rayner added.

The 860-page dossier, first seen by Sky News, included WhatsApp conversations between some senior party staff privately expressing views hostile to Corbyn during his time as leader.

In exchanges following the 2017 general election exit poll, which showed Labour had unexpectedly denied the Conservative Party a majority, staff opposed to Corbyn told each other “everyone needs to smile” and had to pretend “to be upbeat”.

One staff member said of the result, which – while still a loss for Labour – was better than most had predicted: “The people have spoken. Bastards.”

The report also details various disparaging comments, including one staff member referring to an ally of Corbyn as “pube head”. While Corbyn himself was described as a “lying little toerag”

One Labour MP seen to be on the left of the party was called “the biggest cunt out of the lot” while another was called “repulsive”.

The dossier was prepared as Labour awaits the conclusions of an Equality and Human Rights Commission (EHRC) investigation into anti-Semitism in the party.

Corbyn’s time as leader was dogged by claims that he and officials did not act strongly enough against claims of anti-Jewish racism.

The leaked document argued there was “no evidence” of anti-Semitism complaints being handled differently from other forms of complaint, or of current or former staff being “motivated by anti-Semitic intent”.

But it found that “factional opposition” in the upper echelons of the party towards Corbyn contributed to “a litany of mistakes” which hindered the effective handling of the issue.