The Prime Minister says a Labour Party staffer accused of sexual assault has not been working at Parliament for weeks.

Jacinda Ardern told media at here weekly Post-Cabinet press conference that man will not return to the precinct while a review is underway, into an internal investigation that cleared his name.

She says she wants to make it clear she's deeply concerned and incredibly frustrated by the process undertaken by the Labour Party - and obviously by the nature of the allegations.

Ardern says initially the party assured her the allegations were not sexual - but new information contradicts that.

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National has called for Ardern to stand down a man who had worked at the parliamentary precinct, following a detailed accusation of an attack on a Labour volunteer published in the Spinoff.

That came after an investigation by the party into seven formal complaints about the man decided no disciplinary action was needed.

Concerns from the complainants have since seen the party start an appeal process.

The party says none of the complaints investigated were about sexual assault, because the review was not the proper body to do so. The volunteer told the Spinoff she had raised the issue in March but it's not been raised with the man's employer, the Parliamentary Service.