A bid to force Labour to reveal the identities of those it believes leaked the party’s internal report into anti-Semitism has been rejected by the High Court.

Mrs Justice Tipples rejected an application by lawyers for former senior official Emilie Oldknow to release the names of people alleged to have been involved in the unauthorised release of the explosive dossier.

The 860-page internal report, which claimed that “factional opposition” to Jeremy Corbyn hampered the party’s efforts to tackle anti-Semitism, caused a huge political row when it was leaked to the media last year.

It included details of hundreds of staffers’ private WhatsApp messages criticising Corbyn. Some of them expressed disappointment that Labour’s better than expected performance in the 2017 general election would mean he would remain as leader.

Lawyers for Oldknow, who is named in the dossier, had argued that the report was a “politically motivated hatchet job” and that it contained deliberately misleading and improperly obtained private correspondence. She sought the names in order to sue individuals involved.

But in her judgment on Monday, Mrs Justice Tipples said Oldknow’s application for a court order to disclose the names of five individuals “smacks of a fishing exercise” and “individuals who are innocent of any wrongdoing could be identified as a result”.

The judge said she “recognises the strong public interest” in allowing Oldknow to vindicate her legal rights but that did not extend to Labour being “ordered to identify those who it reasonably believed [were] responsible for the leak, or providing a narrative account of the circumstances of the leak” or related documents.

She added that two other investigations into the leak, one by the Information Commissioner’s Office and an independent probe by Martin Forde QC, commissioned by Labour, were ongoing.

“The situation is far from straightforward and whatever conclusions the Labour Party has reached in its internal investigation, it is possible that these conclusions could be modified or changed as a result of the ICO investigation or the Forde inquiry.”

She also ruled that Oldknow will have to pay the Labour Party’s costs in the case, as well as Unite’s costs for written submissions on behalf of five unnamed individuals at the heart of the case. The union’s lawyers represented the five individuals.

Oldknow, once seen as a contender for general secretary of the party, wanted to discover the identity of the leakers in order to sue them individually.

Her lawyers indicated in court that they intended now to pursue the Labour Party as a whole for possible defamation and release of private data.

The court heard that Labour’s “extensive internal investigation” into the leak – which involved “expert forensic analysis” and a third party investigator looking closely at “the activities of a number of Labour Party employees and former employees” – had concluded in mid January.

Labour’s lawyers wrote to five individuals on February 4 to inform them that they were likely to be affected by Oldknow’s application.

The letter said that having considered the evidence the Labour Party had “reached the clear view as to who was responsible for the leak” and it did not intend to actively resist the application before the court requiring it to provide the identities of those responsible for the leak.

But the judge said that matters had moved on significantly since then, “no doubt” because of the intervention of lawyers Carter Ruck on behalf of the five individuals who strongly objected to being named and who vigorously protested their innocence.

Labour then changed its position to saying that while it had come to a “clear view” about who was responsible, that was merely its “subjective” view and there was “no smoking gun” evidence of email or other form that offered definitive proof.

Lawyers for Unite had written to Labour’s lawyers that “on the face of it your client appears to be simply seeking to wash its hands of its responsibilities, by attempting to throw the burden on ‘the court’”.

In her judgment, Mrs Justice Tipples ruled that the disclosure of the names sought by Oldknow would “have the very real potential to cause harm to any innocent persons”.

She said this was because “they will then find themselves threatened with legal proceedings, which they would have to defend”.

“It cannot be overcooked that any such proceedings in this case are likely to be high-profile and defending any proceedings will take time and inevitably involve expensive lawyers […] together with the stress often associated with any litigation,” she said.

“I do not think it is right in principle that a party should be ordered to make a judgement identifying who it ‘reasonably believes’ did such and such a thing. To my mind, a request such as this smacks of fishing.”

She added that a further request for a “narrative” written by Labour in its internal probe was “not a focused request for information” that would lead to the identification of wrongdoers.

“Rather, it seems to me that it’s an advanced request for disclosure, which again smacks of a fishing expedition, so that the claimant can cast around to identify potential defendants [for defamation].”

William Bennett QC, for Oldknow, had offered a “compromise agreement” to remove personal details from any documents provided by Labour. He told the court last week that “anything to do with their private lives can be edited out before it’s provided to the applicant”.

But the judge rejected the move, saying it would be “quite wrong” to because Labour was not satisfied for sure it knew who the leakers were.

Although Oldknow argues that the leak deliberately misrepresented her and was politically motivated, some Labour activists view the dossier’s publication as the act of “whistleblowers” who exposed factional opposition to Corbyn by paid HQ staff.

In a statement after the case, a spokesperson for Unite the union told HuffPost UK: “Unite is pleased the court allowed us to intervene in this application to make submissions on behalf of our members. The principles of confidentiality are vital for workers to have confidence in the workplace.

“We are pleased the court accepted our submissions, dismissing the application of Emilie Oldknow and others as nothing more than a “fishing expedition’.

“We also welcome that the Court has ordered Emilie Oldknow (and others) to pay Unite’s legal costs for the making of those submissions, making clear reference to the importance of Unite’s intervention given that Labour was not offering effective opposition to the Oldknow and others application.” 

The judge refused permission to appeal.

After the ruling, Oldknow’s solicitor, Mark Lewis, said: “We were surprised by the outcome but the case is far from over.”