The police watchdog has found the double tasering of a drunk West Coast man who had earlier been armed with a tomahawk was unjustified.

In a just-released decision, the Independent Police Conduct Authority ruled that police breached policy when a sergeant directed a probationary constable to Taser the man.

"The probationary constable's use of the Taser to contact stun the man twice was a disproportionate and unjustified use of force."

About 9pm on June 20, 2015. Greymouth police were called to a domestic incident between neighbours. A man had come to his neighbour's house, drunk and armed with a tomahawk. When police arrived, they were told the man was no longer armed and had returned home.

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Police knew of the man and his mental health issues. They decided to delay arresting him until the morning when he would have sobered up.

However, police were called back to the man's property at midnight and found the man and his friend, drunk and abusive, sitting in a car. The man was arrested for the tomahawk incident but he and his friend refused to get out of the car.

After a 20-minute struggle, during which pepper spray was appropriately used on the friend, police managed to handcuff the man and his friend and escort them to a police van. When the man refused to move his foot from the van cell door, the sergeant directed a probationary constable to contact stun the man twice with a Taser.

"A Taser can only be used on a person who is assaultive," authority chairman Judge Sir David Carruthers said.

"As the man was simply using his foot to block a door, he was not assaultive. The Taser should therefore not have been used."

The authority also found the sergeant should not have directed the probationary constable to use the Taser in these circumstances.

"The junior officer was put in the unenviable position of feeling like refusal was not an option, given the sergeant's seniority," Sir David said.

The authority also determined that the sergeant should have declared that he had instructed the probationary officer to use the Taser and that he incorrectly recorded that the use of Taser complied with police policy.

Police said they accepted the findings.

Tasman district commander Superintendent Steve Kehoe said it took officers 20-25 minutes to contain and handcuff the man because he was yelling and screaming, resisting, and refused to follow police instructions.

"The man was Tasered once with no effect, before being Tasered a second time as police attempted to get him into a police van cell following arrest.

"We agree with the IPCA that the use of Taser in this instance was unjustified and the sergeant should not have directed an inexperienced officer to contact stun the man because he was not being assaultive.

"We understand the pressure felt by the probationary constable to follow their supervisor's orders and have provided advice around this matter to them."

The sergeant had since resigned and no longer worked for police.

"There have been a number of lessons learned from this incident and we acknowledge the mistakes that have been made and have reviewed some procedures as a result, including the Tactical Options Report (TOR) review process," Kehoe said.