Luxon wants broad inquiry into sacked minister Stuart Nash's correspondence

National's leader Christopher Luxon is calling for an inquiry into sacked minister Stuart Nash's communications across all his previous portfolios.

Nash was already on a 'final warning' when it was revealed he breached Cabinet confidentiality when he emailed details of Cabinet discussions to two businessmen - who were also his donors - in 2020.

The correspondence set out his opposition to a decision on a commercial relief package, of which the donors had an interest in.

Nash resigned as police minister last month for other breaches, including criticising the judiciary.

Before being dismissed, he was Minister for Economic Development, Minister of Forestry, and Minister for Oceans and Fisheries.

Luxon said the latest breach was a "very serious and egregious issue" and on top of the others, broader scrutiny of his correspondence with donors was warranted.

"I think if you were the prime minister seeing a pattern of behaviour - this is the fourth contravention of the Cabinet manual in his case - he also happened to be the Minister for Economic Development, Forestry, or Fisheries, you'd want to know whether he's actually had any other conversations to any other people in any of those portfolios," he said.

"If I was Chris Hipkins, I would want a full inquiry into all of his communications with a whole range of people and his portfolio."

Luxon also called for Nash to resign from Parliament and said he should have no place in the Labour Party caucus if he had indeed lost the trust of the prime minister.

Such a move would trigger a by-election, something Luxon said was simply a logical consequence of imposing standards on government and parliamentary representatives.

"The by-election is just a consequence, or an implication of you holding to an absolute standard.

"The standard is he lost Chris Hipkins' trust, he said that himself last night. He [Hipkins] said the behaviour was an inexcusable, serious, gross breach. I don't understand how he stays in his caucus on that basis. People have been kicked out of his caucus for similar behaviour, and how he can be in Parliament."

Luxon said the implications of Nash's correspondence should be taken very seriously.

"We've never seen anything quite like this I think in Cabinet and breaching of Cabinet protocol like this.

"If you just take a step back what actually happened, Stuart Nash has actually leaked confidential Cabinet information, and also conversations and positions of his peers around that table, to his donors. And you know, that's akin to a type of insider trading, I guess, essentially, he's acting as a lobbyist for want of a better word inside his Cabinet."