The New South Wales police watchdog has cast significant doubt on the use of strip-search powers by officers in the state, arguing common practices including forcing people to squat or move their genitals are not legal.

A new report by the NSW Law Enforcement Conduct Commission found there were “considerable discrepancies” in the way strip-searches have been conducted in police custody and that it had “serious concerns” that changes to police policy had “raised broader legal issues which remain unresolved”.

Released on Thursday, the first report from the LECC’s landmark investigation into the use of strip-search powers in NSW revealed 113 different versions of standard operating procedures used by police when conducting searches in custody, many of which contained “incorrect and inconsistent references” to police powers and legislation.

The investigation uncovered wide-ranging errors in the operating procedures – taken from different commands across the state – including two that instructed police that all prisoners were to be strip-searched. Another 61 of the instruction manuals contained no reference to the legislation guiding strip-search powers, while many that did pointed to repealed sections of the act or contained “confusing” references.

After the LECC began its investigation, the NSW police released new uniform manuals to assist police conducting strip-searches in custody and in the field. While the LECC said those documents “contain many improvements to the clarity and consistency of procedures” they also raised new issues.

The report states the LECC was “concerned” that a number of “key policy positions” in the new manual were “wrong at law”, including the common practice of instructing people to squat or move their genitals during a strip-search.

In October the Guardian reported the now-former head of the LECC, Michael Adams QC, who authored the report published on Thursday, was reviewing whether it is legal for officers to force people to squat during a strip-search.

Police in NSW commonly force people to squat when being subjected to a strip-search, and the new personal search manual published as a result of the LECC’s investigation allows officers to instruct people to squat, lift their testicles or breasts, or part their buttock cheeks.

But in the report Adams found police had “no power” to require people subjected to strip-searches to assist in a search, saying that while it was an offence to hinder police “there is no power reposed in police officers to require a person to actively assist the search, particularly by moving testicles, buttock cheeks, breasts or squatting”.

The finding raises a significant challenge for the current use of strip-search powers by police.

Sam Lee, the head of police accountability at the Redfern Legal Centre, said the report showed that “potentially hundreds of people who have been subjected to an unlawful strip search while being held in police custody”.

“Being placed into police custody is traumatising in itself, but being placed into custody and ordered to strip naked takes the trauma to a whole other level – especially if there was no legal basis for such a search,” she said.

“Updating training manuals and police operating procedures is just not enough. We need law reform to ensure that all people are protected from the trauma of unnecessary and invasive strip searches.”

Hearings conducted by the LECC last year found police commonly force people, including children, to squat or move their genitals when being strip-searched.

In one case, the inquiry heard, a 16-year-old girl was fearful and in tears after she was forced to strip naked and squat in front of a police officer who then “looked underneath” her at the Splendour in the Grass festival in 2018.

In another, a 15-year-old boy said he “shook with nerves” after a police officer told him to “hold your dick and lift your balls up and show me your gooch” during a search at an under-18s music festival in February last year.

Adams noted in his report that the NSW police had subsequently sought advice from the state’s solicitor general “on the question whether a person can be asked to move a part of their body for the purpose of a search”.

“Although the answer given is, in substance, that the suspect can be asked to perform these actions, no opinion was provided as to whether the suspect may be required to perform them or, whether a request having been made, the suspect is under a legal obligation to comply,” Adams wrote in the report.

“Indeed, the opinion conflates the quite distinct notions of request and require, the distinction which lies at the foundation of the problem.

“The commission considers that there is no power reposed in police officers to require a person to actively assist the search, particularly by moving testicles, buttock cheeks, breasts or squatting.”

In a statement, the NSW police noted it had updated its search manuals and said it would consider the recommendations made by LECC.

“The new documents provide consistent guidance to officers about undertaking person searches, with clear references to legislation and police policy,” the statement read.

“As an organisation with extraordinary powers, we understand the need to closely monitor and regularly review the use of search powers to comply with the Law Enforcement (Powers and Responsibilities) Act 2002 and other relevant laws.”

While Thursday’s report focused on strip-searches in custody, the LECC is expected to publish the bulk of its investigation in April. Last week the Guardian revealed that further public hearings had been cancelled after Adams was removed from the position in December.