The use of drug dogs is helping to fuel a massive increase in strip-searches by New South Wales police, often without legal grounds.

A report released on Thursday reveals that in the past 12 years the number of strip-searches conducted in NSW increased almost 20-fold, from 277 times in the 12 months to 30 November 2006 to 5,483 in 2018.

The report, published by the University of NSW and commissioned by the Redfern Legal Centre, warns imprecise legal thresholds defining when an officer is able to conduct a strip-search means unlawful use of the practice is “potentially widespread”.

It cites evidence that in some cases officers use invasive searches to “punish and humiliate” people, and is littered with case studies of people subject to them on suspect grounds.

Those case studies include Zac, a 12-year-old in a regional town who told his school principal he had been stopped by police outside a supermarket and made to pull down his pants and stand in his underwear in front of his friends. Nothing was found.

And Emma, a woman in her late teens who was strip-searched at a music festival despite merely being sniffed by a drug dogs. Again, nothing was found, but Emma was forced to leave the festival and the search, she said, triggered memories of a past sexual assault.

“I felt the same feelings I felt during that assault,” she said.

Advocates have long argued that the wording around strip-searches is too vague, leading to misuse.

Under the Law Enforcement Powers and Responsibilities Act, NSW police are allowed to conduct a strip-search outside a police station if the “seriousness and urgency of the circumstances” make it necessary.

But, the report’s authors argue, that “broadly defined” threshold fails to give police clear guidance on when a strip-search should be carried out, meaning many are conducted without adequate legal grounds.

“Overall, the legislative framework and guidance to police supports the approach that strip-searches are intended to be a last resort for use in exceptional circumstances,” the report sats.

“However, there is ambiguity and police practice has evolved in ways that depart from parliament’s intent that strip-searches be a last resort and only in serious and urgent circumstances; particularly in relation to policing suspected drug possession.”

In fact, the report found that in the 2017-18 financial year suspicion that a person was in possession of a prohibited drug accounted for 91% of all recorded reasons for why police conduct a strip-search.

It found that only 30% of all strip-searches conducted outside of police stations in 2017 and 2018 resulted in charges. Of those, almost 82% were for drug possession offences.

The report’s authors state that “available evidence” suggests the increased use of drug dogs accounts for the massive increase in the use of strip-searches, even though a positive detection from a dog does not constitute the legal criteria for conducting one.

About 20% of all strip-searches in 2017 occurred as a result of a positive indication from a drug detection dog, “but the law and the NSW police special operating procedures require police to have a reasonable suspicion based on more than just a positive indication from a dog before a person is searched on suspicion of drug offences”, the report states.

“Saturation policing with sniffer dogs at music festivals and railway stations or forcing teenagers to remove their clothes in the back of police vans does not make the community safer,” said one of the report’s co-authors, the UNSW lecturer Vicki Sentas. “We need a serious discussion about how best to reform the law so that the police cannot abuse their powers.”

The use of strip-searches in NSW has been subject to widespread criticism and scrutiny.

Last year the police watchdog, the Law Enforcement Conduct Commission, announced it was holding an inquiry into allegations police had abused their strip-search powers. Evidence showed the number conducted by police had doubled.

And last month, at an inquest into MDMA-related deaths at music festivals, the counsel assisting the coroner Peggy Dwyer said she would push for the release of police protocols on when strip-searches could be carried out.

The report also details case studies which, the authors say, show police can use strip-searches “to intimidate targeted groups in the knowledge that there is rarely a serious sanction in the event of an unlawful or improper exercise of power”.

A Redfern Legal Centre solicitor, Samantha Lee, said the “extraordinary rise” in strip-searches showed the law was “not being applied as parliament intended – as a last resort”.

“Strip-searches are an invasive, humiliating and harmful process, and as such, should be only used in exceptional circumstances when no other alternative is available,” she said.

“Updating police education and training material will not suffice. Clear guidance about police strip-search procedure needs to be driven by clear and rigorous law. Without law reform, we will continue to see insufficient training and poorly informed decision-making from police conducting strip-searches.”