' />

The "three-strikes" policy is likely to increase the level of unreported family violence, a survey of ex-offenders and their families has found.

Government officials have also warned "life sentence without parole" could push criminals to kill police and victims to avoid arrest.

The Act Party's three-strikes policy has been introduced as part of the Government's support agreement although Justice Minister Simon Power has conceded it may not make it into law.

An informal survey by lobby group Rethinking Crime and Punishment showed the proposal was likely to increase the level of unreported family violence.

"Rethinking has discussed the three-strikes bill with a group of offenders, ex-offenders and their families and whanau," director Kim Workman said.

"One response, consistent with the three-strikes experience in the USA, is that offenders facing a second or third strike offence, would have little qualms about committing further violent acts to escape apprehension or conviction.

"A recent USA study found that in cities with three-strikes laws, homicide rates increased on average 13-14 per cent in the short term and 16-24 per cent in the long term, compared with cities without the laws.

"But what it also showed, was that victims of family violence would be less likely to report violence against them from their partners, if they knew it would be followed by imprisonment without parole, in the case of a second strike, or 25 years in prison on the third strike.

"The common reaction of the partners was, `I don't want to put my old man away in prison for a long time; I just want him to stop hitting me'."

Confidential documents issued under the Official Information Act and obtained by the Dominion Post also show that the Government has been warned the policy could breach human rights, cause misbehaviour in prison, and clog courts.

It could also lead to judges giving short sentences to avoid the no-parole policy.

Te Puni Kokiri (Ministry of Maori Development) said criminals might attempt to avoid arrest by seriously injuring or killing victims or police.

The Corrections Department said judges may reduce sentences in borderline cases to avoid the policy, while the Treasury said sentences could increase overall, including for less serious offences, as judges brought them in line with increased penalties for repeat violent offenders.

The policy could also result in court delays, with offenders entering fewer guilty pleas and increased appeals to avoid the policy's consequences.

Prisoners with life sentences would also have no incentive to participate in rehabilitation programmes or behave in prison.