An independent inquiry ordered by Keir Starmer into a leaked Labour report on anti-Semitism will aim to complete its work by this summer, the party’s ruling body has agreed.

The National Executive Committee (NEC) endorsed the Labour leader’s call for an external probe into the “circumstances, contents and release” of the controversial internal report.

The leaked anti-Semitism report sparked a furore earlier this month when SkyNews published some of its contents, with many Jeremy Corbyn supporters seizing on suggestions that former party staffers had actively undermined him during the 2017 election.

Starmer and deputy Angela Rayner used their new majority on the NEC to see off attempts to change the remit of the probe after some of its left-wing members demanded that the issue of how the report ended up being made public was not relevant.

The 38-member ruling body also refused to adopt a proposal from Unite to abandon plans to look into just how the secret report – intended for submission to the Equalities and Human Rights Commission – was commissioned in the first place.

It rejected calls for the NEC Officers group – a nine-strong inner core where the Left still has a majority – to approve the new independent panel members, preferring instead for the whole NEC to do so.

The NEC did however toughen up the language in the inquiry’s remit, to focus on alleged “misogyny and racism” of former staffers and to confirm that the party conference had a key role in the affair.

Leftwing members, who warned that those who leaked the report should not be “targeted”, also succeeded in their bid to include reference to protections for ‘whistleblowers’.

The new independent figures heading up the new inquiry will be chosen “in due course”, probably at next month’s NEC meeting, but it is understood that their work is expected to be concluded by mid-July.

The leaked report, which was based on a trawl of 10,000 emails and thousands of WhatsApp messages from former party HQ staff, has led to calls by several MPs for their immediate suspension for alleged racism and sexism and rule breaking.

The 851-page report, which has been seen by HuffPost UK, also concluded that factional hostility towards Corbyn amongst ex-staff contributed to “a litany of mistakes” that hindered the effective handling of anti-Semitism complaints.

It claimed there was “no evidence” of anti-Semitism complaints being treated differently to other forms of complaint and talked of the need to “question the validity of the personal testimonies” of former members of staff who had complained that anti-Semitism was institutional within the party.

But much controversy centred on private WhatsApp messages that the dossier contained, with some showing staffers making derogatory remarks about Diane Abbott, Dawn Butler and others. Corbyn and fellow ‘Trots’ were repeatedly singled out for criticism by ex-staffers too.

Several former officials have in turn now joined forces in threatening legal action, claiming breach of data protection, privacy and libel and arguing their words were taken out of context. The party faces a possible multi-million pound lawsuit over the way private information was included.

The Labour leader has pledged to crackdown hard on anti-Jewish racism, declaring on his first day in the job that he would “tear out this poison at its roots”.

However, the row over the report threatens to overshadow his first few months in post, testing to the limit his bid to unite the party and bring together its different wings.

Starmer and Rayner have made clear they will not tolerate any racism or misogyny. During the NEC meeting Starmer stressed that there would be “consequences” for anyone who broke party rules.

Labour MPs like John McDonnell, Richard Burgon and other members of the Socialist Campaign Group of MPs have demanded disciplinary action against former staff members.

In a letter issued ahead of the meeting, the Campaign Group urged the NEC to focus on the allegations against senior staff “rather than on the targeting of whistleblowers who have brought the revelations to light”.

Shadow Treasury minister Dan Carden signed the letter, which said the report had “shocked and caused hurt to large numbers of Labour members and supporters”. It demanded the independent probe should not be “kicked into the long grass”.

But several members of the NEC told HuffPost UK that it was right to look into exactly how the report had entered the public domain and how such an important document was commissioned without the NEC being aware of its existence.

One NEC member said it was the leadership’s “first victory”. “Keir and Angela got what they wanted on their terms of reference and pretty much on the timescale they wanted,” they said.

Another added the Left were “roundly defeated” during the four-hour meeting. “All their main amendments were defeated including the attempt to limit the investigation to the culture and practices of the staff and not to look at how the report was commissioned and the leak.”

But one member of the NEC stressed that Starmer himself worked hard to get compromise and made clear that following the rules and due process was the key.

A Left member added they were “very happy with the result”. “It’s fair. Toughening up on whistleblower protections, specific mentions of racism and discrimination included.”

A spokesperson for the Labour Party said: “The National Executive Committee has today agreed the terms of reference for the independent investigation into the circumstances, contents and release of an internal report.

“The NEC will meet again in due course to agree the individuals who will be appointed to lead the investigation.”