Labour Party president Nigel Haworth says he has handled complaints to the party "professionally", but Prime Minister Jacinda Ardern is waiting on a review to determine any wrongdoing.

And Haworth continues to reject claims that he was told about a serious sexual assault allegation involving a Labour staffer.

Meanwhile, National Party deputy leader Paula Bennett says Ardern has been "absolutely deaf" to the complainants, and that at least three complaints were made about sexual misconduct.

The Prime Minister told reporters this morning that she repeatedly asked the Labour Party whether the complaints involved claims of sexual misconduct, and was repeatedly told there were none.

That has been contradicted by complainants, with an email trail back to March 2018 and reported claims of verbal evidence about the claims given to a panel of the Labour Party's ruling New Zealand council.

Labour has been rocked by claims that a 19-year-old complainant was subjected to a sexual attack by a male Labour staffer in February 2018, which was revealed in an article on The Spinoff.

Lawyers for the staffer say the claims are "without foundation".

The party investigated seven formal complaints earlier this year and concluded no disciplinary action was needed.

Maria Dew QC is now reviewing that process and, at Ardern's request, the substance of the complaints.

A key question is whether Haworth misled Ardern, and his future now depends on the findings of the review by Dew, expected in four weeks.

An open letter to Ardern has emerged calling for Haworth to resign, but he told reporters this morning that he was confident he had handled the process "professionally".

He batted away further questions, refusing to say when he was first told about sexual assault claims.

"I am making no comment on the current processes. I am bound by confidentiality.

"I am not resigning. I am going to look at my situation as the process develops. If I have been found at fault, I will consider my position."

The 19-year-old complainant told The Spinoff that she had told Haworth of her claims of sexual assault during a meeting in a private room at Wellington Central Library, and then told the party's investigating panel both verbally and via email.

But Haworth rejected that.

"The serious allegation of a sexual assault, outlined in The Spinoff article and in other media, was not provided to the president and acting general secretary at a meeting in the Wellington Central Library or subsequently to the Labour Party Investigation Panel," he said in a statement this afternoon.

Ardern said that if Dew's report found failings on Haworth's part, he will resign.

This morning Newshub handed Ardern a copy of an email from March last year to a member of the investigating panel that purportedly outlined a complaint of a sexual nature.

"I've asked for every piece of evidence that's gone to the party to go to the QC," Ardern replied.

She said she only learned that the complaints were sexual in nature on Monday.

Asked about an email from complainants to media in July and media stories about allegations of a sexual nature in August, Ardern said she had directly asked questions of the party.

"I continually through this process have queried with the Labour Party whether or not they had received complaints that individuals claimed to be sexually assaulted, and I was told 'no'.

"Clear allegations have been made here that claims of sexual assault were taken to the Labour Party and not acted on. That is directly in contradiction to what I've been told. That is not good enough. I need clarity."

Ardern said the allegations, where the staffer is alleged to have pinned the woman to the ground and attacked her at his home in February 2018, were "extraordinarily distressing".

She said there was no question that Labour had not handled this well, and had not learned from the sexual assault allegations from last year's Young Labour summer camp.

National Party deputy leader Paula Bennett says the Prime Minister has been "absolutely deaf" to complaints about a Labour staffer. Photo / Mark Mitchell

Paula Bennett said she spoke with some of the current complainants this morning, and they had told her that several Labour MPs, including Grant Robertson and Kiri Allan, knew about complaints of a sexual nature.

But Allan said she was not aware of such allegations.

"If the party knew of sexual assault allegations, then I would expect that this matter would have been conducted in a very different way."

Robertson would not say what he did or did not know about sexual assault claims, saying it was important to let Dew do her review.

Bennett said she had also seen email evidence that complainants had told the ruling council's panel about sexual assault allegations, adding that Ardern was being "absolutely deaf" to the complainants.

"[She] asked a couple of questions of one staff member and thought that was enough for her not to go there," Bennett said.

"Twelve different people have made [formal and non-formal] complaints, and I'm informed that at least three of them were sexual assault, and the others were around intimidation, bullying and actual violence.

"I've got no doubt that they [the Labour Party] have probably been selective in what they have told her, but that in itself shows that they're trying to protect her so much that, what, she can't handle the truth? Did they learn nothing from the [Young] Labour sex camp scandal?"

Bennett said one complainant had reported seeing the staffer on the parliamentary precinct.

Ardern said the staffer had not accessed parliamentary buildings since August 6, but conceded that he still could have been in the precinct.

"Of course I would want to know if anyone else was enabling someone to access the building when they had been explicitly told they should not."