Simon Bridges wants an independent inquiry into his expenses leak that has forced him to defend the roughly $114,000 he clocked up travelling around the country between April and June.

Mr Bridges says the expenses aren't the issue as they would have been released on Thursday regardless, but he is more concerned about the fact they were leaked and the ramifications for those in Parliament.

"I have discussed matter with the Speaker and my very clear view is that there needs to be an independent comprehensive investigation away from the Speaker, parliamentary services and Government.

"I think it has to be comprehensive, led by someone such as a High Court judge that I and National agree with," Mr Bridges told media this afternoon.

Although the National Party leader says he is "very confident" it wasn't a National MP that leaked the expenses, he is prepared to go where the evidence takes the inquiry.

"I want to get to the bottom of it," he said.

Earlier Prime Minister Jacinda Ardern "categorically" ruled out that Mr Bridges' expenses leak came from Labour.

"We've sought assurances from Ministerial services who manage this information that none of the Opposition's numbers were shared with anyone but them," Ms Ardern said. "They've given us that assurance."

"We've had it confirmed no-one in Labour actually ever had access to that information. The only groups as I understand who will of had access will be the Opposition themselves and the speaker."

She said even if Labour had access to it, it would be "totally inappropriate" to leak it.

