Critics also demand shake-up of organised-crime-fighting unit after the Red Devils and Dotcom cases.
The police will "reassess" aspects of their undercover operation against the Red Devils gang, but are still facing calls for a shake-up of the organised-crime-fighting unit that oversaw that operation and the controversial Dotcom raid.
Police were this week on the receiving end of a stinging High Court ruling which found they breached the court process by faking the prosecution of an undercover officer to protect his cover as he infiltrated the Nelson gang.
Justice Simon France's ruling has seen drug and other charges against 21 members of the gang and associates thrown out of court, although police may appeal.
Assistant Police Commissioner Malcolm Burgess last night said police would "reassess aspects" of the undercover operation after the judgment which found they committed a "fraud against the courts".
"We are reviewing our processes to ensure this does not happen again," Mr Burgess said.
The operation against the gang was overseen by the Organised and Financial Crime Agency of New Zealand (Ofcanz) and headed by Detective Inspector Grant Wormald, who also headed the joint raid on internet millionaire Kim Dotcom's mansion for the agency.
President of the Criminal Bar Association and former undercover policeman Tony Bouchier said the agency's involvement in the two high-profile cases raised questions about its methods.
"Certainly if you look at the Dotcom case and you now look at this particular case you might be forgiven for thinking they're more result driven than they are concerned about the way in which they achieve those results."
While the agency's involvement in the Dotcom case could be seen as "a series of blunders", the Red Devils case was more serious.
"It's different in nature, it's about maintaining the integrity of our independent judiciary and the criminal justice system in New Zealand."
Mr Bouchier called for an inquiry into Ofcanz by either the Independent Police Complaints Authority or a Queen's Counsel "to look not only at the organisation and what in fact is going on there but also to look at the Red Devils case specifically to see if there's any criminal wrongdoing by anybody in that organisation".
Labour Party justice spokesman Charles Chauvel said he previously had some concerns about Ofcanz because the National Government set it up within the police rather than as a standalone statutory agency as Labour originally envisaged when the agency was first mooted in 2007.
"... it's reasonably clear that some oversight is required."
Labour would push for Ofcanz to be reconstituted as a standalone agency.
Police Minister Anne Tolley yesterday defended Ofcanz and its methods.
"I have no doubts that Ofcanz are doing their very best to fulfil their function, which is to make sure that we do not have organised crime continuing to operate in our country.
"We cannot tie both hands behind their backs and expect them to be able to break into and break up these very sophisticated criminal organisations."
Former undercover police officer Andrew Harland said the officers in charge of the investigation should have been aware their actions were not acceptable.
Mr Harland said that when he was working undercover between 1999 and 2001, judges took very seriously any action that could be seen to "deceive justice".
In 1999, Mr Harland applied for a licence to run a South Auckland second-hand store as a way to be involved in the criminal underworld, as part of a police inquiry. But the application was held up by a judge who was aware he was an undercover police officer.
"You'd think that would be a minor thing. But the judge wouldn't just sign the [order], because he was looking into the implications of deceiving justice."
- additional reporting APNZ