LISTEN ABOVE AS JACINDA ARDERN SPEAKS WITH MIKE HOSKING ABOUT THE LEAK. 

Parliament's Speaker Trevor Mallard wants answers over the leak of National leader Simon Bridges' travel expenses.

Mallard will request the list of people who have access to the full expense list, after Bridges' bill was leaked last night, ahead of the full list's public disclosure next week.

National and Labour have denied leaking details of the National leader's travel costs.

Newshub reported last night that MPs' expenses for travel and accommodation, which it had been leaked, showed Bridges' bill for the last three months came to $113,973. Most of that, $83,693, was spent on Crown limousines.

The expenses are due to be made public later this week.

Prime Minister Jacinda Ardern said today she did not have access to the expenses of the Opposition.

"Even if I did, that's not the kind of politics that I engage with or that I'll allow the Labour Party to engage with," she told Newstalk ZB's Mike Hosking.

Ardern said she didn't know who did leak the information.

"Parties have made available to them their own expenses so that's probably a question better asked of the National Party."

Ardern said Bridges had acted within the rules and added that when she saw her expenses after first becoming party leader, she was surprised how high the figure for surface travel was.

"I remember wanting to change my behaviour as a result of that. These numbers, sometimes, when you think you're just out doing your job you suddenly receive an expense and some of the figures can be extraordinary. It certainly threw me the first time that happened."

Bridges told Radio NZ yesterday that the information he had so far suggested the expenses were not leaked by anyone in the National caucus.

"Already I'm getting a sense that this is not from my party, that there's something different at play here. As I say though, I don't have perfect information on that. It may be over time we see what the truth is but it does seem pretty strange."

Bridges, who recently wrapped up a countrywide roadshow to raise his profile said he had been working hard to get to the regions and understand their issues.

"It's really important for National given that we represent ... nearly half of New Zealanders all around the country, that I get out and do this hard mahi [work]."

ACT Leader David Seymour called for an investigation into the leak.

"It is outrageous that a bureaucrat from the Parliamentary Service saw fit to leak details of Mr Bridges' travel expenses to media.

"This smacks of a politically motivated attack. New Zealanders expect an independent, professional public service. This leak is an unacceptable act and must be investigated."

Speaker Trevor Mallard, who has access to the expenses, last night tweeted that he had asked for a list of who else did.

He had also asked for an explanation as to why his and Bridges' expenses were "bloated" by the previous quarter's figures.