National backbench MP Chris Penk has released a 30,000 word missive criticising the government's "lockdown lunacy" and calling its initial response to Covid-19 "shockingly slack" and "incompetent".
The position appears at odds with his leader Todd Muller who has described the government's handling of the crisis as "overall impressive".
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Penk unveiled his self-published book - 'Flattening the Country: the real story behind Labour's lockdown' - on his National website on Thursday evening, alongside an offer to send out signed copies for $20 a pop.
The book is heavily critical of the Covid-19 response, arguing that a poorly prepared and panicked government "set about destroying the village that is New Zealand in order to save it".
"It was only supposed to be the curve that got flattened, not the whole country," the book begins.
The Helensville MP argues New Zealand benefited from "good luck" in the early days, and that its performance had been "average in international terms".
"Our government's initial reaction to news of this global pandemic was shockingly slack. They told us that they were 'alert but not alarmed', when 'conscious but incompetent' would have been closer to the truth."
The book goes on to critique "Labour's particular form of lockdown lunacy", arguing it was too harsh and was unnecessarily extended.
"Whole industries have been led like so many lambs to a no-longer-non-essential slaughterhouse."
Prime Minister Jacinda Ardern last week told Parliament she stood by all of her decisions, saying the results of the response spoke for themselves.
Penk's book is closer in tone to that of former National leader Simon Bridges than that of the new leadership team.
Bridges was hit by an avalanche of vitriol on social media in April after publishing a Facebook post critical of the government response.
The backlash helped fuel arguments within the caucus for a leadership change and was a factor in Bridges' eventual ousting in May.
Muller, in his first speech as leader, sought to distance himself from Bridges' style, saying he would avoid "opposition for opposition's sake".
"I am the first to admit and acknowledge that the government's handling of Covid-19 was overall impressive," Muller told reporters.
Speaking to RNZ, Penk said he had discussed his plans for the book with the party's leadership going back to when Bridges was still in charge.
"The positions that I have stated in the book are consistent with the messages that National has been putting out from the start."
He said he was not worried about any potential backlash from the public.
"A large number of people are fearful about expressing a view that is anything other than the perceived wisdom, the single source of truth, and they don't want to be ostracised as not being part of the team of five million.
"Frankly, the bullying tactics that have been applied to others don't hold any weight with me."
National deputy Nikki Kaye told reporters she was "very relaxed" about Penk's publication.
"We live in a world where we have freedom of speech, and there are National MPs that feel very strongly around what has happened," she said.
"Chris is entitled as a local MP ... to take a view around the government's response in terms of Covid."
Penk entered Parliament in 2017 after winning the safe National electorate of Helensville, previously held by former leader Sir John Key.
The MP - ranked 41 in National's caucus - was previously a navy officer and lawyer.