Smoking will be banned in all prisons from next year, the Herald on Sunday has learned.

Corrections minister Judith Collins is expected to announce this week that a 12-month preparation plan will be rolled out that should see all prisons go smoke-free by July next year.

Department of Corrections bosses found taxpayers could be liable for lawsuits from prison guards exposed to inmates' second-hand smoke.

The potential threat of legal action was heightened after the Government's decision to "double bunk" inmates in a single cell, raising the possibility of non-smoking prisoners suing the Government for being housed with smoking inmates.

The dangers of legal action were found after Collins instructed Corrections staff to investigate a ban, and its success rates overseas.

They found tobacco was used as currency inside prison and was the cause of disputes. Further reasons for the ban included the use of cigarette lighters and matches to melt plastic into which blades could be embedded, turning cell possessions into weapons.

Anti-smoking Maori Party MP Hone Harawira supported the move but warned a total ban could lead to an outbreak of violence among prisoners.

"I'm mindful of the fact that you can make people pretty scratchy when you cut things off. One thing I do know is that inmates won't be allowed to go outside for a smoke," he said.

"I like to think that the guys in there rebuilding their lives are also rebuilding their health. Prison tends to be a place where people come out healthier than when they go in, they don't have the opportunity to do a lot of the things they were doing before."

Health benefits were also advocated in the Corrections report. A 2005 Health Ministry study found that two-thirds of all prisoners smoked, far higher than the national average.

A spokesman for Action on Smoking and Health said the organisation was "very supportive" of the plan.

"We find 80 per cent of smokers want to quit anyway," said Michael Colhoun.

But he said prisons had a higher smoking population than the general public and wanted to see a large-scale quit plan introduced before the ban.

"It wouldn't be fair to do this without providing a comprehensive cessation service."

Corrections is planning to ramp up its quit smoking programmes for prisoners.