A criminologist is calling on the government to invest in addiction programmes aimed at treating the causes of crime, rather than spending billions of dollars locking more people up.
The government recently rolled out changes to sentencing, including encouraging the use of cumulative sentencing for people who committed offences while on bail, parole or in custody.
It was the first step towards fulfilling National's coalition agreement with New Zealand First - which could see the prison population double and would cost Corrections billions.
But an alcohol and drug counsellor said all that money could be spent on rolling out more drug courts which were proven to reduce re-offending.
In National's coalition agreement with New Zealand First, it agreed to make cumulative sentences for prisoners who commit offences on parole, bail or while in custody compulsory.
That was instead of concurrent sentences and meant they would be sentenced to serve that time after they completed their first sentence.
But Ministry of Justice modelling found this could increase the prison population by 10,000 people, with most only having committed minor crimes.
Criminologist and alcohol and drug counsellor Roger Brooking said this was a huge waste of money.
"They are rehashing old strategies that have been tried in the past, and simply do not work. In the meantime, we have drug court in Auckland which reduces re-offending by 86 percent and actually keeps people out of prison."
The money spent on locking people up could be much better spent on rolling out more alcohol and drug treatment courts, Brooking said.
People who were facing a sentence of three years or less and had an alcohol or drug problem were eligible for these specialist courts.
They would have to plead guilty, agree to treatment for their addiction, and check back in at the court regularly while being drug tested.
Right now, there were only three of them in the country - two in Auckland and one in Hamilton.
Brooking would like see them rolled out nationwide - at a cost of around $2 million per court, per year to run.
He said they were a bargain.
"That is an absolutely drop in the bucket, compared to what the government is going to be spend being tough on crime and locking up more and more people."
A 2019 evaluation of the courts found those who completed the programme were 86 percent less likely to re-offend within one year.
That dropped to 56 percent within two years and 42 percent within three years.
About half the participants in the evaluation did not complete the programme, and were sentenced to prison instead.
Similar rehab programmes run inside prisons reduced re-offending by less than 5 percent.
In 2019, there were plans to expand the drug and alcohol court programme by opening a new one in Hawke's Bay.
But that plan was scuppered by the Covid-19 pandemic.
There was also a Ministry of Justice report the same year casting doubt on the court's effectiveness.
Justice Minister at the time, Andrew Little, who was responsible for the court's roll out, questioned the accuracy of the report.
"There were criticisms at the time that it wasn't that robust, and it certainly seemed to fly in the face of what those in the system were saying who were responsible for seeing offenders going through the alcohol and other drug courts."
The court's pilot programme was started by National in 2012.
In a 2019 parliament exchange, then opposition MP Mark Mitchell criticised Little for being slow to expand the programme.
"Why did it take two years for the minister to commit to extending the previous government's very successful alcohol and drug treatment courts?" he asked.
But it was not a priority for the current coalition government, with a spokesperson for Justice Minister Paul Goldsmith saying it had a very busy justice work programme and there were no plans to roll out more drug courts.
Brooking said the current plan to change the sentencing act to make jail terms longer would not deter criminals and was not backed by evidence.
"In fact, there is evidence to the contrary. That prisons are in effect a university for crime ... it damages people, it traumatises people. They come out in a worse space than they went in, and they're more likely to continue to re-offend."