The Supreme Court says some former psychiatric patients will be allowed to sue the Government over allegations they were abused in the 1970s.

The court today released a decision saying it had partially allowed an appeal by six former Porirua Hospital patients.

The court said the six informal patients, as opposed to committed patients, treated after March 31, 1972 could continue their legal action to sue the Government in the High Court.

They were entitled to costs of $15,000.

The decision is seen as likely to determine the course of proceedings for a group of 280 claimants who were admitted, with their agreement, for treatment at various psychiatric hospitals around the country in the 1960s and 70s.

The former patients, who cannot be named, claim they were abused in various ways; hospital staff physically assaulted and sexually abused them, they were not protected from other patients, were subject to inappropriate electro-shock therapy and long periods of solitary confinement.

The defendant is the Crown Health Financing Agency, formerly the Residual Health Management Unit, the Crown entity now responsible for historical liabilities for alleged mistreatment.

W ellington lawyer Sonja Cooper said it was a significant decision for the 80 to 90 per cent of her 200 clients who were patients post-March 1972.

It meant barriers in the Mental Health Act, which gave immunity to psychiatric staff and the Crown against liability, did not apply to people who were informal patients after March 1972, she said.

The process started in 2002 and the first claims were filed in 2004, she said.

"This has ambled its way through two levels of the High Court, then the Court of Appeal, then through to the Supreme Court, so now we will actually be able to start progressing cases through to trial, so that's great.

"For a lot of our clients this has already been a seven year process."

Ms Cooper said none of the claims had been through the court system yet but it involved "reasonably high levels of damage".

A conference will be held later this month to determine what action will now be taken, she said.

The Court of Appeal earlier ruled restrictions on bringing civil proceedings against those acting under mental health legislation applied to all patients, including informal patients.

The restrictions required that plaintiffs obtain leave of the Court to bring the proposed proceedings showing that there was substantial ground for contending that hospital staff had acted in bad faith or without reasonable care.

Applications also had to be made within six months of the alleged actions giving rise to the proceedings.

However, the Supreme Court decided that correct interpretation of the legislation meant restrictions on bringing proceedings ceased to apply once the responsibility for psychiatric hospitals moved from the Government to hospital boards (later Area Health Boards) in 1972.