Penal reformers say the "three strikes" legislation passed by Parliament is a blot on the judicial landscape and is diverting attention from rehabilitation.
The Sentencing and Parole Bill was passed into law yesterday on a vote of 63-58, with National and ACT supporting it.
It means that on conviction of a third serious violent offence a maximum sentence will be handed down with no parole.
Judges can also order that murderers with no previous convictions will never be freed if their crime if their crime is particularly heinous.
Kim Workman, director of Rethinking Crime and Punishment, said today there were 8200 people in prison and only about 3 percent would be caught by the three strikes legislation.
"Of the other 97 percent who are languishing in prison, 80 percent are illiterate, 40 percent have diagnosable mental illness and 80 percent have drug and alcohol dependency issues," he said.
"Of the additional $700 million allocated from the budget to prisons and probation over the next four years, $11 million - about 1.5 percent - will be spent on rehabilitation in the from of drug treatment.
"That will mean that 1000 of the 6000 prisoners requiring drug treatment will receive it by 2014. The rest of the money will go to keeping more people locked up."
The legislation was an ACT Party initiative and its justice spokesman, David Garrett, said it should mean a drop in crime of between 10 percent and 20 percent.
"I would expect a marked reduction once the policy is fully in place," he said today.
"People cannot harm members of the public when they are in jail."
Labour, the Greens, the Maori Party and United Future opposed the bill.
Maori Party MP Hone Harawira said it would not reduce crime at all.
"Just by putting a guy in jail for the rest of his life doesn't stop the fact that other people are in the same conditions and are likely to start heading down the same path," he said today.
NZPA