Two female former Labour staffers have accused the party of making damaging statements to the media about a sexual harassment case, demanding in a leaked letter that the party acknowledge they were asked to sign gagging clauses.

The two former aides have written to the national executive committee (NEC), the party’s governing body, asking it to address the allegations at a meeting on Tuesday.

Two sources said they believed it was likely that the NEC meeting on Tuesday would receive a long-delayed report into allegations of bullying, racism and sexism within the Labour party.

But a Labour spokesperson said the report by Martin Forde QC had not yet been received by the party on Monday afternoon. Another party source said the report had been delayed multiple times despite being expected in previous months.

Its eventual release is likely to reignite bitter tensions in Labour over the conduct of staff from different party factions during Jeremy Corbyn’s time as leader.

The two former staffers, Georgie Robertson and Laura Murray, have given evidence to the investigation, which was commissioned by Keir Starmer after the leak of a document containing private WhatsApps that exposed deep factionalism in Labour’s efforts to combat antisemitism.

But the report’s publication has faced a number of setbacks, including legal action against the party by some of those named in the original leaked document, an investigation by the Information Commissioner’s Office (ICO) into data breaches, and Labour’s decision to sue five former staffers who it alleges leaked the original document. The legal actions and ICO investigation are ongoing.

Robertson and Murray, who worked underCorbyn, wrote to the NEC on Monday demanding that the party retract statements given to the Mail on Sunday about a sexual harassment case.

The accused staff member, who has not been named, has since departed.

Robertson and Murray are two of the five accused by Labour of leaking the original report containing the unredacted private WhatsApps – which they deny.

When they resigned from the party, the women refused to sign legal agreements with a confidentiality clause after making official complaints about the alleged harassment, and chose to resign without payouts. Their story was first reported by BBC News, which said it had seen the official documents including an initial complaint, formal grievances and official correspondence.

The former official accused of harassment was temporarily suspended but denied the allegations. Labour issued a statement to the Mail on Sunday, which revived the story last weekend, saying no non-disclosure agreements (NDAs) “have been proposed to any member of staff alleging sexual harassment since Starmer took over as leader”.

But in a letter to the party seen by the Guardian, Murray and Robertson cite detailed evidence of the party’s most senior lawyer setting out confidentiality clauses to protect the party and the individual they accused.

Robertson and Murray said the party must apologise for this “categorically false statement … which has further compounded the significant hurt and distress we have suffered”.

In their letter, which was also sent to Starmer, the deputy Labour leader, Angela Rayner, and the party’s general secretary, David Evans, the pair say they “do not see how the NEC can fully consider recommendations on tackling sexist and discriminatory culture and practices within the party, without the party taking responsibility for this attempt to publicly undermine our credibility and cover up what happened to us”.

They alleged they were contacted by other former employees who claimed they signed agreements containing similar clauses relating to experiences of bullying or discrimination.

The letter contains detailed correspondence between the party lawyer and the lawyers for the two women, including excerpts from emails where the pair attempt to retain the right to take legal action against the individual. The party’s lawyer is quoted as saying that cannot be an exemption.

In the letter, the pair called it a “bogus distinction” that such a confidentiality clause would not amount to an NDA.

Labour declined to comment on the letter’s specific allegations, citing confidentiality. A spokesperson said: “The Labour party takes any complaints of sexual harassment extremely seriously, which are fully investigated and any appropriate disciplinary action is taken in line with the party’s rules and procedures.”