Jacinda Ardern's brushing off claims from Simon Bridges she was behind the Speaker's decision to axe the inquiry into the leaking of the National leader's expenses.

The Prime Minister says Labour wasn't sent the text claiming to be a National insider who leaked the material.

Ardern says Trevor Mallard acted on his own, without any help from her.

She says cancelling the inquiry was his call.

Ardern says she sought assurances that the leak did not come from Labour.

"In fact, the information never came to us. It always struck me that this was more than likely an internal matter for the National Party."

On Friday, it was confirmed that the police know the name of the leaker after they investigated the text messages. 

Asked whether police should either confirm or deny it was a National MP, Ardern said it is their decision.

"That is for the police, so the operational matters we've had no knowledge of their involvement and nor should we. Ultimately how they choose to manage their involvement is ultimately for them, and that is as it should be."

Police say they will not be disclosing the person's identity for privacy reasons.