The orchestrated arrest of an undercover police officer working in Nelson to boost his criminal standing was unusual, a court has heard.

"I think it would be fair to say it's a rare occurrence, but it does happen," National Crime Manager Detective Superintendent Rodney Drew said in the High Court at Nelson yesterday.

Drew was called to give evidence in a pre-trial hearing involving several people arrested in a police operation targeting Nelson's Red Devils Motorcycle Club.

Lawyers representing the defendants want the charges thrown out, arguing that police abused the court process when they arrested the undercover agent, who went by the assumed name Michael Wiremu Wilson.

Wilson, who infiltrated the Red Devils in Nelson, was arrested near the Red Devils' headquarters in Natalie St on May 29, 2010 and charged with possessing equipment to cultivate cannabis.

Police had earlier searched a storage unit he rented in Motueka to find the equipment.

Nelson District Court staff and some police officers were unaware that the charges against Wilson were fake.

Drew said strict police policies existed for carrying out such a prosecution, and it was necessary to get it signed off by the Chief District Court Judge. He knew of one other arrest of an undercover agent in similar circumstances in 2002, but it was possible there were other cases.

Drew said he had ordered a review of the police policy for arresting undercover agents in orchestrated scenarios, pending the outcome of this case.

The court yesterday heard that Wilson and another undercover officer, who was posing as his de facto partner, were in the process of shifting to the Nelson region.

Drew said the orchestrated arrest of Wilson was necessary for his protection, as he had been threatened by a gang member. It was also necessary to enhance his appearance of criminality.

Chief District Court Judge Russell Johnson, who has since died, approved the fake prosecution.

Drew said the meeting with Judge Johnson on May 31, 2010 was over in five minutes.

The judge knew that the prosecution was false, but did not know details of who the undercover agent was or where he was working.

Drew said he could have provided the answers to those questions if Judge Johnson had asked.

Under cross-examination by lawyer Pip Hall, Drew said Wilson was challenged by Red Devils member Michael Tulouna on May 4.

He was asked by defence lawyers whether Tulouna was a paid police informant, but replied that in keeping with police policy, he could not confirm or deny this, even though Tulouna had since died.

Defence lawyers also asked Drew whether undercover agents were often threatened.

He said he was satisfied that the threat from Tulouna was genuine. Wilson was under a "constant current of suspicion" from the gang's members.

Hall asked MDrew if he had considered whether police were involved in conspiring to pervert the course of justice.

Drew said he was satisfied that police were acting in good faith and in accordance with police policy, and if there were any issues, they would be examined in court.

Detective Sergeant John Mackie, of Wellington, who was involved in supervising the undercover operation, told the court that Wilson did not end up pleading guilty as planned. Red Devils members recommended that he see a lawyer they knew, who advised him to defend the matter. Police went along with this to maintain his cover.

Wilson failed to appear in court twice to enhance his credibility. Warrants were issued for his arrest.

The charges against Wilson were eventually withdrawn when police wound up the operation against the Red Devils in March last year.

Several people face drug and other charges in relation to their arrests. The pre-trial hearing continues today.

- © Fairfax NZ News