Hamish Walker, the Clutha-Southland MP, fell on his sword on Wednesday, hours after National leader Todd Muller wrote to his party board asking them to disendorse him.

Mr Walker received confidential information from a former party boss, Michelle Boag, and then shared it with at least three media outlets, saying he wanted to show vulnerabilities in the government's information storage.

No media outlets chose to publish the information.

Mr Muller, leader of National, called the behaviour "completely unacceptable" and wrote to his party's board asking them to consider his membership.

"This is not the National party I lead," he told Radio NZ.

"It's not the culture I expect from my team and bluntly there needs to be consequences."

Mr Walker appeared set to fight for his political career, getting legal advice that he had not committed a criminal offence, but then withdrew his candidacy for re-election at the 2020 poll.

"I wish to thank the people of Clutha-Southland who I have loved meeting, assisting and representing over the past two and a half years," he said in a short statement.

"I sincerely apologise for my actions. I will be making no further comment."

The scandal is a further setback for National ahead of the September 19 election, already well behind in the polls as it challenges Jacinda Ardern's Labour for government.

Deepening the party's embarrassment, Mr Muller attacked the government for the leak before discovering his own MP was the source, saying it was "a reminder these guys can't manage important things well".

In a further plot twist, Radio NZ also reports Mr Walker leaked them the advice in an attempt to back up a claim of Mr Walker's which was derided as racist.

Mr Walker argued against the expansion of mandatory isolation facilities into his electorate, which are compulsory for Kiwis arriving home from abroad.

"These people are possibly heading for Dunedin, Invercargill and Queenstown from India, Pakistan and Korea," he said, comments that were widely interpreted as a dog-whistle.

Mr Walker then offered to prove his allegations to Radio NZ by supplying the confidential information - contradicting his public claim that he did so to show up government weaknesses.

The scandal, first revealed on Tuesday night, further engulfed National on Wednesday as Ms Boag was revealed as a campaign team member of deputy leader Nikki Kaye.

Ms Boag, who was National party president two decades ago, resigned from that role and as Auckland Rescue Helicopter Trust acting chief executive - the capacity in which she accessed the confidential information.

Australian Associated Press