Bad behaviour in Rimutaka Prison's high security units has continued for years

The Inspectorate Office has released a report on the Upper Hutt Prison - after a surprise inspection.

A 2017 inspection found problems with violence and staff being overly familiar with inmates.

No progress has been made to reduce gang influence, intimidation and assaults on inmates and staff.

And a regime installed to manage the problem has resulted in prisoners spending too much time in the cells.

Police have been carrying out an unrelated investigation into possible corruption at the prison, since July.