National health spokesman Michael Woodhouse told leader Todd Muller on Tuesday evening that he was also sent Covid patient data by Michelle Boag.

Woodhouse confessed this morning he was sent four unsolicited emails from Boag between June 21 and 25 which contained patient details, but it was not the same information that was sent to disgraced MP Hamish Walker.

A party spokeswoman said today Woodhouse told Muller this on Tuesday night.

But the next day, Muller was specifically asked by reporters "have you checked with Woodhouse, specifically, whether he received that same information from Boag".

"No," replied Muller and a reporter asked "why not?"

"It's very clear from our perspective there's a conversation that's occurred between Michelle Boag and Hamish Walker. We are confident from what we can see that the issue here relates to Michelle Boag and Hamish Walker."

He said it wasn't accurate to say he didn't know whether other MPs in National had access to that information.

"We are confident from what we can see that the issue here relates to Michelle Boag and Hamish Walker ...You've heard very clearly from the participants that the issue was between Michelle Boag and Hamish Walker."

At no point in yesterday's media stand-up did Muller mention that he knew Boag had sent Covid patient information to Woodhouse.

Muller said he had not sought assurances from his other MPs about whether they knew about confidential data held by Boag or Walker.

"She's made it clear publicly her only interaction was with Hamish, and no doubt that'll get confirmed in the process with Michael Heron QC," Muller said.

Asked again if he had spoken to Woodhouse and if Boag was a Woodhouse source, Muller said: "No, I don't really understand where you're going with this. We've had a situation over the last 48 hours. It's very clear that I think it was totally inappropriate what occurred. Hamish Walker has now paid the price."

The spokeswoman said Muller didn't say something yesterday because "we had to look at what that information was and the nature".

"We needed to assess the information."

In his confession this morning, Woodhouse said he was sent four emails from Boag in her capacity as acting chair of the Auckland Rescue Helicopter Trust.

But he believed it was different information from the subject of the Government's inquiry into the leak, but was similar insofar as it contained patient details.

"I was led to believe it was circulating among a number of other health agencies.

"I recognised that the information in those emails was private so I did not share it with anyone else and I subsequently deleted them."

On Tuesday evening, a day after the Government launched an inquiry into who leaked the details of 18 active Covid cases to the Herald and two other media outlets, Hamish Walker confessed that he was behind it. Boag admitted she was his source.

On Wednesday midday, Walker announced he wouldn't stand for re-election in the Clutha-Southland seat.

Boag announced this morning she had resigned from the National Party because the last few days "have underscored for me the unhealthy relationship I have developed with politics".

She said she had devoted much of life to supporting the National Party.

"Unfortunately this passion has put me on a self-destructive path.

"This was confirmed for me as I wrote to Michael Heron QC last night to advise him that towards the end of June I had sent several emails to Michael Woodhouse comprising notification of a small number of then new Covid19 cases.

"My decisions to share this information were wrong, driven by my distorted view that providing that information would help the National Party to hold the Government to account. In fact it was harmful, not helpful, and it is time that the National Party and I parted ways."