A call by National leader Simon Bridges for an independent inquiry headed by a figure such as a High Court judge into the leaking of his expenses to the media is "extravagant in the extreme", New Zealand First leader Winston Peters says.

Parliament's Speaker Trevor Mallard is already looking at the leak and is considering whether a further, forensic examination is needed of a document containing the information which was given to Newshub ahead of its public release on Thursday.

He expected to reveal his decision later this afternoon.

Bridges said yesterday any inquiry needed to be independent from Parliament.

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But Peters told reporters today the inquiry did not need the services of a High Court judge.

"It doesn't require that level of scrutiny, frankly. An ordinary graduate from law school could work this one out. There's probably about 55 suspects."

Peters was referring to the 55 members of the National caucus, excluding Bridges.

"It's extravagant in the extreme. First of all he spends all this money then he shouts out for an inquiry after the Speaker has announced one," Peters said.

Bridges has confirmed that all National MPs had access to the information, as did the Parliamentary Service and the Speaker's Office.

But he is confident the leaker is not one of his MPs. "I very much doubt it. I'm incredibly confident it's not going to be a National MP," he said yesterday.

Prime Minister Jacinda Ardern has denied any of her MPs were involved.

The expenses document given to Newshub revealed that Bridges' accommodation and travel for the last quarter totalled more than $100,000, the majority of it on Crown limousines.

Bridges has defended the figure, which come after his nationwide tour to raise his profile, saying 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)."