Police are appealing a High Court decision to throw out charges against 21 Nelson gang members after police tried to falsely prosecute an undercover officer to boost his credibility within the group.
Last week Justice Simon France ordered a stay of proceedings against the group, who were facing a range of charges including drug offences and being part of an organised criminal group.
The Solicitor General confirmed today that the decision would be appealed.
Police were investigating the emerging Red Devils Motorcycle Club, who they suspected were about to become a chapter of the Hells Angels.
During a crackdown, dubbed Operation Explorer, police bosses became concerned that an undercover officer known in the gang as Michael Wiremu Wilson was about to be exposed.
To strengthen his credibility in the gang, police arranged for a fake search warrant of his lock-up in which they had placed apparently stolen equipment and drug paraphernalia.
Police forged an illegible signature of a court deputy registrar, and arrested Wilson.
Wilson appeared on several occasions before judges, who all believed they were dealing with a genuine case.
Soon after Operation Explorer ended, police sought to have Wilson's charges withdrawn.
Justice France said he believed police thought they were acting legitimately, but a letter police gave to Judge Johnston about the situation would have been ``wholly inadequate'' to alert him to the realities of what was involved.
There was fundamental and serious abuse of the court's processes by the police, he said.
Operation Explorer was overseen by Detective Inspector Grant Wormald, who also headed the joint raid on internet millionaire Kim Dotcom's mansion for the Organised Financial Crime Agency.