Professor Sir Peter Gluckman, chief science adviser to the prime minister, delivered a report in 2018 into the acceptable levels of methamphetamine in contaminated Housing NZ homes.

A bombshell report shows there is no real risk to humans from third-hand exposure to houses where methamphetamine has been consumed.

This means tens of thousands of homes have been needlessly tested and cleaned at the cost of millions of dollars, with some demolished and left empty.

The study by the Prime Minister's Chief Science Advisor Peter Gluckman found that New Zealand authorities had made a "leap in logic" setting standards. Essentially, a standard used overseas based on what "clan labs" should be cleaned to was now being used as a trigger to start cleaning here, despite no real health risk at that level.

SCOTT HAMMOND/FAIRFAX NZ A meth contaminated house in Marlborough.

"In the absence of clear scientific and health information, there has been an assumption among the general public that the presence of even trace levels of methamphetamine residue poses a health risk," Gluckman said.

"There is absolutely no evidence in the medical literature of anyone being harmed from passive use, at any level. We can't find one case."

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Gluckman said testing and cleaning still made sense when there was suspicion that methamphetamine had been produced on a property - but this was more to do with reassurance.

He said a "moral panic" around cleaning and remediation had occurred only in New Zealand. If science had been involved earlier in the policy-making process this could have been avoided.

Mould was a much larger health risk to tenants than meth residue.

ROBERT KITCHIN/STUFF Chief Science Advisor to the Government Peter Gluckman couldn't find a single case of a meth home that was a health hazard.

In response to the recommendations, Housing Minister Phil Twyford has announced new standards and less stringent standards will be set for houses within the next year - with Housing NZ immediately changing its policy.

The current level of 1.5 micrograms per 100cm2 was only useful as a barometer of what to get houses cleaned to after manufacture - not as a trigger to start decontamination, the report said.

A measure of 15 micrograms per 100cm2 - 10 times higher - would make more sense as a trigger.

ROBERT KITCHIN/STUFF Housing Minister Phil Twyford with Chief Science Advisor Peter Gluckman. "We're looking at a 1000-fold safety factor minimum in our recommendations, for a naked toddler crawling around the floor licking every bit of the floor up to several hours a day," Gluckman said.

Gluckman said he wouldn't be worried about "toddlers crawling around on the floor" until the meth residue reached the level of several hundred micrograms per 100cm2 - not the current standard of 1.5 - and this was based on a 300-fold safety buffer.

He stressed the government's recommendation was still very far below a level where it could become dangerous.

"We're looking at a 1000-fold safety factor minimum in our recommendations, for a naked toddler crawling around the floor licking every bit of the floor up to several hours a day," Gluckman said.

240 state homes sitting needlessly empty would be put back into use within weeks, and Housing New Zealand would save up to $30m a year on testing, Twyford said.

"The great majority is testing and remediation was completely unnecessary," Twyford said.

A review into how the standards were set would also be carried out by Consumer Affairs Minister Kris Faafoi.

PETER DRURY/STUFF In the "reasons" section of the Tribunal decision the adjudicator has written "During [the man's] tenancy Housing New Zealand were advised by the Auckland District Health Board to test his tenanted premises for methamphetamine contamination."

"Very significant sums of money have been spent on testing and decontamination of houses that are thought to have been contaminated by methamphetamine," Twyford said.

"Housing New Zealand alone in the last fours years has spent $100m on testing and remediation.

"Large numbers of homes thought to have been contaminated were left empty in the middle of a housing crisis."

Twyford commissioned the report soon after coming into Government, but Gluckman stressed it was totally independent.

Former Social Housing Minister Paula Bennett welcomed the report and said she had long pushed back against Housing NZ's approach.

Bennett was minister over 2014-16, when hundreds of state housing tenants were evicted over meth residue, with some charged thousands of dollars in costs.

"I lose count of the number of times that I questioned [Housing New Zealand] about it. To the point that I was told as a minister that I was on the edge of getting involved of day to day running of the technical issues of a crown entity," Bennett said.

"I found it incredibly frustrating that there were houses empty when people needed them so desperately. I wanted people in them.

"I think that Housing NZ had a genuine concern about the health and safety particularly of children. Now we know they went over the top in trying to make sure they were safe."

She did not believe the previous Naitonal-led Government had contributed to a sense of moral panic around methamphetamine, despite its strong law and order messaging around the drug.

"It is an insidious disgusting drug," Bennett said.

"I do think there was a level of hysteria around meth contamination."

She said both she and former Prime Minister Bill English felt the standard was too low but they were not technical experts.

"I just instinctively didn't think it was right."

However, in several news stories at the time Bennett and English said they approved of the Housing NZ regime.

English said the agency was "rightly taking a firm stance on the health risks posed by meth, and will continue to do so for as long as it is detected in its properties" in 2016.

And Bennett told Newshub in 2016 there was "no evidence" Housing NZ had evicted tenants unfairly.

Twyford has repeatedly talked up the more compassionate approach Housing NZ had taken to state homes where traces of methamphetamine were found.

In December, he said the approach would be changed, with tenants will mostly be offered help instead of eviction when traces of meth are found in their homes.

He did not rule out compensation for those wrongly kicked out, and said they should be at the top of waiting lists for new houses.

The social housing provider's review of their drug policy started before the election, with National saying it realised the thresholds for meth testing were set too high and there needed to be "a sensible arrangement".

In response to the report, Housing NZ has immediately set its standard at 15 micrograms per 100 cm2, up from 1.5 micrograms.

Properties that Housing NZ suspected were used for meth production or "very heavy use" would be tested and still decontaminated if the level was above 15 micrograms per 100cm2.

"Housing NZ will continue to refer all suspected meth lab activity to Police," chief executive Andrew McKenzie said.

"The decision to adopt these levels was made factoring in the findings in the CSA report that they are unlikely to lead to any adverse health effects for our staff, tenants and contractors."

"Our position on meth testing and decontamination is we work to the guidelines set by experts in this field and we work to that advice."

METH TESTER SAYS REPORT IGNORES SCIENCE

Miles Stratford, director of meth testing company MethSolutions, said the report presented no new evidence and ignored people who had come forward wanting to tell Gluckman about their issues with meth contamination.

"You're never going to find evidence if you don't go looking for it," Stratford said.

"What we've got is a whole bunch of scientists who can't agree and a report that aligns with Government policy."

Research analyst Anne Bardsley at the advisor's office, who worked on the report, rubbished this claim, saying she reached out many times to try and find the evidence behind the "real world" cases companies came forwards with.

"It always fell apart," Bardsley said.

Stratford said more research should be done and jumping to conclusions based on the current science was "reckless".

He quoted "real-world research" by Australian scientist Jackie Wright - who is employed by a meth testing agency - which suggested children living in places with tests between 11.7 and 26 micrograms per 100cm2 had the same amount of methamphetamine in their hair as adult users had.

Bardsley said she had talked to Wright for over an hour about her research - which involved a single situation where meth was being produced, not a home in which meth had only been smoked.

"It was clearly a former lab," Bardsley said.

Stratford also cautioned that health risks were only one of the reasons real estate investors obtained meth tests.

"Meth users in a property create significant financial risk to an investment property owner,' Stratford said.

"If they have to pick between paying the pipe and paying rent the pipe is going to win, every time."