As many as 20 people may be wrongly in New Zealand's jails, says the retired High Court judge who looked into the Peter Ellis Christchurch creche case for the Government.

Sir Thomas Thorp is calling for an independent authority to be set up to identify miscarriages of justice, the number of which he says is underestimated.

His recommendation follows a two-year study of the nature and incidence of miscarriages of justice, and the way New Zealand and comparable countries deal with such claims.

Sir Thomas, whose interest in the topic arose from reviews he did for the Government, including work on the Ellis case, said that, based on British experience, "up to a score" of New Zealand inmates may be wrongly jailed.

His research includes analysis of 53 applications to the Justice Ministry claiming miscarriages of justice from 1995 to 2002. Of these, he classified 26 per cent as "raising issues that clearly required careful investigation".

Sixteen per cent were "plainly without merit", while 58 per cent had "sufficient potential to require some further investigation".

In August, Parliament's Justice and Electoral Committee also recommended the establishment of a body to look into miscarriages of justice.

Sir Thomas' report, titled Miscarriages of Justice, has been published by the Legal Research Foundation, a non-profit body associated with Auckland University's law faculty. The university is holding a seminar on the report next month.

Though it was impossible to make reliable estimates of the number of miscarriages of justice, Sir Thomas said he found nothing to indicate the rate in New Zealand would be significantly different than in Britain. His estimate that there may be 20 people wrongly imprisoned was based on the experience there.

There were proportionally fewer complaints of miscarriages in New Zealand, something Sir Thomas believed was explained by New Zealand's system being reactive, whereas all people convicted of crimes in Britain were made aware of the independent review process available there. As well, Maori and Pacific Islanders used the existing processes much less than Pakeha.

Sir Thomas told the Weekend Herald the reason for Maori and Pacific Islanders' low use of the system may be that they felt most strongly that they were not understood by the justice system.

"I think that there is in our racial difficulty a sense that people are not understood, which is complex and not open to simple resolution. But, surely, changing from the present self-generating system - which requires complainants to hold their hand up and come up with a written petition or claim - to a system which actually goes out to make sure that all convicted people are aware there is this authority and it will help them formulate a claim if need be, that should make some difference."

In his report Sir Thomas said a "fully independent and appropriately staffed and resourced authority" should have the task of identifying miscarriages and putting them forward for reconsideration by courts. That should include investigative capability.

The authority should seek means to reduce the ethnic imbalance of claimants, identify causes of miscarriages in New Zealand, recommend means of minimising their occurrence, and assess compensation for wrongful convictions.

According to published reports of inquiries Sir Thomas has carried out for the Government, he concluded David Bain's conviction for the murder of his parents and siblings was safe but he had misgivings about Peter Ellis' conviction.

National's justice spokesman Richard Worth said he was in favour of an independent commission.

Mr Worth said Ellis was a good example of the labyrinth of procedures parties could get caught up in as they tried to prove a miscarriage of justice.

Criminal Bar Association president Peter Winter said an independent body was necessary.

"There has been a climate of setting up institutions that prosecute, including the Serious Fraud Office, and greater authority for serious crime provisions. It is time there is a counter-balance to redress those who are wrongly convicted," Mr Winter said.

"There is nothing worse than languishing on an improper conviction, particularly if you feel as though you can't communicate adequately with the system."

A spokesman for Attorney-General David Parker said last night the minister had not seen the report, but because it was by a retired High Court judge it warranted his attention and he wanted to read it.

Causes of miscarriages of justice overseas:
* Misconduct by police and prosecutors
* Lawyers not doing their job properly
* Incorrect eyewitness identification
* Forensic errors
* Using prison informants
* Public and political pressure.