The announcement of the return of the 10 year passport has been met with confusion by a terrorism expert.

Internal Affairs Minister Peter Dunne said yesterday the government has listened to New Zealanders and adult passports will again be valid for a decade, once required law changes are made.

The 10 year adult passport price will cost $180, which means an average saving of more than $90 over the 10 year validity period.

The Labour Government cut the validity period back to five years in 2005, blaming it on an increased terrorism risk.

University of Canterbury dean of law Chris Gallavin says even though there's been investment in better security in New Zealand, things are worse now than a decade ago.

"With the rise of ISIS [Islamic State] we could say the world is more threatened by acts of terrorism than what it perhaps has been in the past," he claims.

Gallavin believes there could be an ulterior motive involved, including lobbying from other countries.

"This might a push on behalf of the airlines," he said. "It might be a push on behalf of Tourism New Zealand, it could be international pressure with the practice of issuing passports by other countries."

John Stace, one of the organisers of campaign group NZ Ten, is questioning why the move was ever made, and says the justification given in 2005 of increased terror risk still doesn't stack up.

"Many countries who have moved to five years have beaten us back to ten years so I do not think there was ever a proper and valid reason for moving to a five year passport."

Stace insists his claim isn't over - he's now going to lobby for a brightly coloured passport instead of the black ones we use now.

"As many passports are lost or mislaid as stolen. That is because leaving a dull passport on a park bench or a railway station is quite easy they way they are, the colour they are at the moment."