The Labour party is in turmoil. It has just elected a new leader, Keir Starmer, who campaigned on the basis of party unity and ending factionalism. There was a sense from this result that members wanted a period of calm. But a deeply controversial internal report was leaked over the weekend to journalists and then distributed on social media. The effect has been to escalate factional warfare and intensify the toxic relationships between different groups within Labour.

The report is the result of an internal investigation into the work of Labour’s governance and legal unit in relation to antisemitism. Created by party staff, it pulls together an estimated 10,000 emails, thousands of messages exchanged on work accounts, and the contents of two WhatsApp group chats apparently created by senior management in Labour headquarters. However, it will not be submitted to the Equality and Human Rights Commission that is currently investigating antisemitism within the party, as party lawyers have reportedly decided that it is not within the scope of the external probe.

Some have assumed that the document, dated March 2020 and written by staff working in the era when Jeremy Corbyn was leader and his ally Jennie Formby the general secretary, provides evidence that Labour’s antisemitism problem is fictitious. That is not the conclusion of the report. Instead, its primary claim is that disciplinary cases were indeed poorly handled by the party; that this was not a mishandling of antisemitism complaints in particular but of all complaints in general; and that the situation has improved under Formby.

The parts of the document that have gained most attention are those focused on the “hyper-factional” environment existing within party HQ between Corbyn’s election in 2015 and previous general secretary Iain McNicol’s departure in February 2018, according to the report. It paints a truly horrible picture of an atmosphere dominated by politically motivated cruelty. There will be party members who recognise the nastiness of comments from the heated debates in their own local parties. But the report is shocking because the messages are alleged to come from senior staffers. It says the comments made about colleagues include “total mentalist”, “bitch face cow” and “pube head”, while Diane Abbott is mocked for crying in a toilet. There is also evidence that purports to show a staffer hoping that a named young member with mental health issues “dies in a fire”.

The other aspect to the factionalism described in the report, putting aside the vitriol, is the hope apparently expressed by anti-Corbyn staffers that Labour would not be electorally successful. The document contends that those in charge of party operations wanted the Liberal Democrats to win the 2017 Manchester Gorton byelection, created a “secret key seats team” to prioritise general election spending in seats held by MPs on the right of the party even when they were “safe”, and were disappointed when Corbyn’s Labour did better than expected in the 2017 general election. The messages in the report show discussion of a “Trot hunt” during the 2015 leadership election to prevent new party members voting for Corbyn.

The reason given for exploring these examples of factional warfare at the very top of the party is two-fold. The report argues that anti-Corbyn staffers were more interested in work that would benefit their side of the internal war than in processing complaints. And it asserts that HQ’s opposition to the leader’s office “disproves allegations that Corbyn’s office had influence over [the general legal unit’s] work”. This is key in light of the 2019 BBC Panorama programme on Labour antisemitism, in which staffers said Corbyn’s office had asked to be directly involved in the complaints process.

The rest of the report dives into the failings of Labour’s disciplinary system, asserting that the unit “did not properly log complaints”, that there was no record of action being taken on serious cases, and that “well-evidenced” antisemitism complaints were dismissed as “spam”. It also sets out the details of particular cases – controversially so, due to the implications for data protection now that it has been leaked.

If the Panorama documentary told one side of the Labour antisemitism story, as Corbynites say that it does, this internal report shows the other side. Its claims will undoubtedly also be questioned. An independent investigation into the contents and release of the report has already been announced by Starmer. What is undeniable is that complaints have been mishandled due to a toxic internal culture, and that this has caused deep hurt – to the Jewish community, and to party members who worked hard for the Labour party with little reward.

Less than two weeks into his leadership, Keir Starmer has his work cut out. Difficult decisions that will have repercussions for Labour’s future – from procedural changes in HQ to trying to bring about a fundamental shift in party culture – lie ahead.

• Sienna Rodgers is editor of LabourList