Newshub can reveal the Labour Party has been forced to review an internal investigation into bullying, sexual harassment and sexual assault by a Labour staffer.

It follows complaints the investigation process was botched and traumatising for the alleged victims. At least four people have resigned from official party roles and cancelled their membership as a result.

The complainants say the party's done nothing to improve its processes since the sexual harassment allegations at last year's Young Labour summer camp.

Prime Minister Jacinda Ardern is aware of the allegations. Finance Minister Grant Robertson also knows some details, so do two other Labour MPs.

Following the Young Labour summer camp allegations in 2018 of sexual assault, underage drinking, bullying and harassment, Labour promised it would do better.

The Prime Minister said in August last year, "We need to do things differently".

An inquiry by lawyer Maria Austen recommended sweeping changes including to the party's bullying, sexual harassment and assault policies.

But Newshub has spoken to five people who say nothing has changed since then.

When asked if the Prime Minister has lived up to her promise, one of the complainants said: "Not at all."