Labour is to indefinitely delay publication of the findings of a highly charged inquiry into a leaked report on antisemitism and internal party culture under Jeremy Corbyn, amid concern it could prejudice an investigation by the information commissioner. In a leaked letter seen by the Guardian, the chair of the inquiry, Martin Forde QC, told Labour’s general secretary, David Evans, that the seriousness of the investigation meant the inquiry findings could not be published. An unredacted report on Labour’s handling of antisemitism claims, leaked in April last year, reignited the row within the party over its handling of disciplinary cases and led to party members’ suspension. The report included hundreds of private WhatsApp messages from named staff members, many of them expressing hostility towards Corbyn or his close allies and bemoaning Labour’s better-than-expected performance at the 2017 general election. Labour’s then general secretary, Jennie Formby, reported the leak to the Information Commissioner’s Office to look into potential security breaches. After Keir Starmer’s election as party leader, he ordered an independent inquiry under Forde. The Guardian understands that the ICO had also received complaints not only about the original leak of the private messages but also the passing of the private messages to the Forde inquiry, which some of the subjects have claimed was also a breach of data protection laws. However party sources said it was only the original leak which is subject to investigation. In his letter, which was read out to the party’s national executive committee (NEC) on Thursday, Forde said his report could only be published after the ICO had concluded its investigations, which could include looking at whether criminal acts were committed. The Guardian understands that senior Labour figures have expressed concern at the seriousness of the ICO’s inquiries. Labour is already subject to legal proceedings by numerous staff members named in the report with the first stage of the court hearings set to begin in two weeks. Forde wrote in his letter that the panel had been “working extremely hard to deliver our report in the early part of this year”, but he added: “We have recently been made aware, however, that as a result of those potential breaches, the ICO has indicated it is making inquiries, pursuant to its statutory duties. “Having regard to the possible direction and outcome of those inquiries, we are therefore concerned that the publication of our report could prejudice those inquiries and our ability ultimately to deliver our final report to the NEC.” Forde said he had considered whether any aspect of the report could be published and concluded that it could not. “We consider there is a real risk that even partial disclosure of our report and findings could have the potential to prejudice the ICO’s work. As soon as its inquiries are completed, and resolved, we will provide a report,” he said. He hit out at “ill-informed speculation as to the perceived delays” and said the inquiry had considered more than 1,000 submissions from party members and affiliates. “Any suggestion that I or my panel have been subject to pressure from the party regarding the delivery, content and conclusions of our report is entirely refuted. In fact, the party and its officers have not sought to influence its content in any way,” he wrote. • This article was amended on 12 February 2021. After publication, Labour party sources stated that the ICO investigation covered only the initial leak of private messages, and not the passing of those messages to the Forde inquiry. Text has been changed to reflect this.