A National-led Government would keep the worst criminals at high risk of re-offending behind bars, even after they've finished their sentences.

Making the announcement in New Plymouth today, Prime Minister John Key said the offenders would remain at a secure facility under a new "civil detention order" until the Parole Board was convinced they were safe for release.

Law and order spokeswoman Judith Collins said applications would be made to the High Court for offenders to be held in custody after finishing their jail sentence.

The new orders were expected to apply to between five and 12 offenders over a 10-year period.


"These will be offenders who have been clinically assessed as being at imminent risk of serious sexual or violent re-offending - people too dangerous to be set free in our communities," Ms Collins said.

National would also introduce pre-parole screening to weed out prisoners unlikely to be granted parole.

The policy is aimed at relieving the burden on victims of crime, who are often re-victimised every time they make a submission to the parole board, and at making better use of the parole board's resources.

But it has been criticised as denying justice to prisoners who would still have a chance at parole.

The Government has previously championed this change at the Sensible Sentencing Trust conference last year, where it received support from parole board chair Sir David Carruthers.

"Many [parole hearings] are easily predictable. We know that, and so does the inmate, and yet by law, we have to meet and have this discussion. [A screening process] would prevent, we think, a lot of victim distress, it would save us a lot of time and money," Sir David said at the time.

Ms Collins said more than 650 parole hearings were held every year for prisoners who have not completed part of their offender plan, meaning they had little chance of being granted parole.

Under National's policy, police would be encouraged to work more closely with partner organisations and improve responses to the abuse of elderly people.

In New Zealand, organisations such as Age Concern receive around 1000 referrals each year alleging some form of elder abuse or neglect.

The policy also includes:

* Increasing penalties for producing, trading or possessing child pornography.

* Introducing random drug and alcohol testing where being drug and alcohol-free is a condition of bail, home detention or other community sentences.

* Making drug and alcohol treatment available in all New Zealand prisons and doubling the number of prisoners participating in work to release programmes. Currently drug and alcohol programmes are available in nine of New Zealand's 19 prisons.