Yesterday, the Law Commission president, Justice Sir Grant Hammond, pleaded with a parliamentary select committee to scrap the proposal which, he said, would really make the public service "faceless".
It was a matter of "grave and even constitutional importance", said Sir Grant, who is also an Appeal Court judge and sat on one of the Couch cases.
Under the bill as it stands, "Ms Couch could never have sued the probation officer who made the acknowledged and disastrous mistakes which were made in her case".
Sir Grant said the planned law would also bar teacher unions from suing the Ministry of Education over the Novopay failures.
He conceded that public servants needed to be protected from the lawsuits of "crackpots and entirely meritless cases".
Under the old law, government staff could be sued but under an indemnity their department had to pay if the public servant was found to have been negligent.
But the effect of a Supreme Court decision in 2010 was that public servants have neither immunity from lawsuits nor an indemnity, Sir Grant said. He urged the committee to overturn the Supreme Court decision and return the law to what everyone thought it was before - an indemnity for public servants, not an immunity.
He said the Cabinet paper giving the background to the proposed law did not address the issue of individual accountability.
"It pre-supposes in what has been said that if an official is, for instance, grossly negligent in the performance of his or her duties that that official should never be able to be named as a party or challenged in a lawsuit.
"The lawsuit simply couldn't be filed because the immunity stops you dead."
A letter would have gone from Crown Law to Mrs Couch's advisers saying: "You can't sue at all. It's immunity. You don't get off the ground."
The probation officer in the Couch case was never named.
The bill in which the immunity is proposed, the State Sector and Public Finance Reform Bill 2012, is being considered by the finance and expenditure select committee.
New Zealand First leader Winston Peters said he totally supported the bid by the Law Commission to get rid of any immunity and reinstate indemnity. Although he did not want to see in New Zealand the sort of litigation that was so prevalent in the United States, he said, it was very hard already for some people to get justice.
Mr Peters referred to the cases of "bad blood" in the 1990s in which more than 200 people got very meagre out-of-court settlements because blood wasn't properly tested.
In other countries, negligent public servants had gone to prison.
