Police are refusing to comment on revelations that notorious motorcycle gang the Hells Angels have patched over a Nelson bikie gang.

In its latest New Zealand expansion move, the infamous group has allowed the Red Devils motorcycle club of Nelson to become a "hang around" chapter, according to sociologist and gangs expert Dr Jarrod Gilbert.

"This move was entirely predictable," said Dr Gilbert writes in his new blog.

"The Red Devils' links to the Hells Angels are well known, and having served a mandatory period as an associate group, they have been given leave to wear some identifying Hells Angels insignia."

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In time, it's likely it will become an official chapter, joining those in Auckland, Wanganui and the Hells Angels Nomads chapter.

But local police are refusing to speak about the latest move.

"We have no comment to make in relation to the suggested activities of these groups," a spokeswoman said.

The Hells Angels first emerged in Auckland in 1961, the first chapter to form outside of California.

The Red Devils formed in Nelson five years ago.

Dr Gilbert says their modest ranks were made up of members of the Nelson Bays Motorcycle Club.

Police soon launched Operation Explorer, fearing the gang was about to become a Hells Angels chapter.

An undercover agent infiltrated them, but as Dr Gilbert pointed out, the forging of documents by police has meant the case is still mired in the courts.

He said the addition now of the Hells Angels brand "is likely to assist in swelling the ranks of those wanting to join."

Dr Gilbert spent 10 years with the country's most notorious gangs researching his book Patched: The history of Gangs in New Zealand.

In the last four years gangs have expanded rapidly, at a rate not seen since the 1970s.

"Outlaw clubs, for certain people at least, have returned to vogue," said Dr Gilbert.

"Brotherhood, booze and bikes. The outlaws, it seems, are back."