A senior Hells Angel is trying to get a drug charge dropped because of a fake police prosecution of an undercover officer.

Philip Ernest Schubert, a former president of the Mt Eden chapter of the motorcycle gang, was charged with offering to supply methamphetamine after a covert police sting.

He was arrested as part of an 18-month inquiry in which an undercover officer infiltrated the Red Devils in Nelson, recognised as a feeder gang to the Hells Angels.

But a deal struck between senior police and the chief district court judge to allow the officer to be arrested in a bid to protect his assumed identity and "ensure his continued safety, divert suspicion and enhance the appearance of criminality" is now the subject of a legal challenge.

The police asked the permission of Judge Russell Johnson for the prosecution of Michael Wiremu Wilson to go ahead, as the undercover agent would have a complete defence under the law.

Several lawyers, including Auckland barrister Eb Leary, have criticised the deal as a "sham" prosecution.

The Herald can reveal that Mr Leary is Schubert's defence lawyer. The 65-year-old Schubert is charged with offering to supply the undercover agent with Class-A drug methamphetamine.

Mr Leary will apply to the High Court at Auckland today to challenge the evidence in an attempt to have the charge dismissed.

He said the legal action could also affect charges against the Red Devils' members in Nelson,

Detective Superintendent Rod Drew would not comment on the Schubert case but said police targeted organised criminal groups and used undercover agents to do that - which was very dangerous work.

"They need to be supported in any way possible."

- Staff reporter