One of the members of Labour's investigating panel has broken his silence to say that he was not told about a sexual assault complaint against a former Labour staffer, either verbally or via email.

Simon Mitchell was one of three members of Labour's investigating panel that looked into seven formal complaints about the ex-staffer and decided in July that no disciplinary action was needed.

The ex-staffer, who was employed by Parliamentary Service and worked in the Labour leader's office, quit his job last week but continues to say he has done nothing wrong.

His resignation followed that of Nigel Haworth, who stood down from the Labour Party's presidency after Prime Minister Jacinda Ardern challenged him over his handling of the complainants and the harm that the party's process had caused them.

Maria Dew QC is now reviewing the issue after complainants said the process was unfair and the sexual assault complaint was ignored.

A tumultuous week kicked off for Labour when a 19-year-old volunteer detailed an allegation of sexual assault in an article published last Monday in The Spinoff.

She subsequently released email correspondence to The Spinoff that she said outlined her sexual assault claim to the panel, both in March and in June, adding that she also told panel members about the assault verbally.

But Mitchell said that was untrue.

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In a statement, he said the woman emailed him on a March morning before she was due to testify before the panel to ask if he could print a timeline testimony that she wanted to read to the panel.

Mitchell said he told her to email the document to Labour's assistant general secretary Dianna Lacy, who printed a copy and gave it to the complainant.

"When the complainant met with the panel, she read from a document taking us through her concerns. She did not provide us with a copy of that document.

"At no point did she say that she had been sexually assaulted or tell us about the events that are described in The Spinoff article."

Mitchell said he has checked the document that was sent to Lacy and it did not contain any details of the sexual assault allegation that was outlined in The Spinoff.

"I met with the complainant again on May 29 to clarify the allegations and the matters we were investigating," Mitchell said.

"At no time during that meeting did she say that she had been sexually assaulted by the subject of the complaint or disclose the events that are the subject of The Spinoff article."

After following up with her about further documentation, Mitchell said she emailed him three documents on June 11, including one that she referred to as her testimony, none of which contained any reference to a sexual assault.

Mitchell said that she emailed him on June 17 and thanked the panel for their hard work.

The woman alleges that the ex-staffer attacked her in February 2018, and that she told Haworth about the attack in October 2018, and then told the investigating panel verbally and in documents attached to an email about the nature of the attack in March this year.

Following Haworth's claim of knowing anything about a sexual assault claim, the woman released the June email to The Spinoff, which reported that the email contained a clear reference to the sexual assault.

Mitchell said he was gravely concerned by these reports.

"On becoming aware on the complainant's allegation that she had provided me with details of the assault on her both in person and in attachments to emails sent to me on March 9 and June 11, I have had my computer forensically examined," Mitchell said.

The March email had no attachment, and none of the attachments sent in June referred to a sexual assault, he said.

Mitchell's lawyer Penny Swarbrick declined to send the Herald a copy of the emails and attachments, with personal details redacted.

Prime Minister Jacinda Ardern said this afternoon that the terms of reference for the review by Maria Dew QC had been finalised but would not be released at the request of the complainants.