Research into New Zealand prisons has found more than a third of inmates are in voluntary segregation.   

The report from Independent Research Solutions says the influence of gangs on prison culture has grown significantly in the past decades.  

It finds inmates are being categorised as being gang members or non-gang members - with the latter being the worst off.  

Author Jarrod Gilbert told Mike Hosking prisoners must either join a gang, fend for themselves, or be separated.   

He says the massive increase in voluntary segregations is unconsciously establishing two prisons within a prison.  

Gilbert says the Department of Corrections may hold the keys to the prisons, but on the inside it's a different story. 

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