The NSW Police Commissioner can no longer force officers to answer questions about their conduct on duty after a landmark ruling preserved an officer's privilege against self-incrimination.

In what was seen as a test case for police procedure, Justice Christine Adamson ruled it unlawful for the commissioner, Andrew Scipione, or anyone on his behalf, to direct a Coffs Harbour officer, Constable Errol Baff, to answer questions about a critical incident.

Curtailed: Andrew Scipione, Commissioner. Credit:Sylvia Liber

Constable Baff had claimed the protection of the common law privilege not to incriminate himself.

Constable Baff discharged his weapon on May 31, 2011, shooting a Victorian woman.