The Inspector of the Independent Commission Against Corruption has blasted the watchdog as a "poor loser" after it urged the Baird government to pass laws to reverse a devastating High Court ruling on the scope of its powers.

Former Supreme Court judge David Levine, QC, who oversees the commission, cautioned Premier Mike Baird against "any knee-jerk legislative reaction that will serve to render the ICAC a second police force or crime commission".

The comments ratchet up the pressure on the commission, which is reeling from a four-to-one majority decision of the High Court that it had no power to investigate Crown prosecutor Margaret Cunneen, SC.

In its first substantive comments since the decision on Wednesday, the corruption watchdog said the ruling would kill off current investigations and call into question previous convictions flowing from its inquiries.

It warned the result "has the potential to involve the state of NSW and the commission in costly and protracted litigation involving persons who have been the subject of corrupt conduct findings" under the section of the ICAC Act at the heart of the Cunneen case.

Mr Levine said his "initial reaction to ICAC's statement was that it was as blustering a statement by a poor loser as it was an improper and dismissive attack on the judgment of the highest court in the land".

He launched an audit of the commission's investigation into Ms Cunneen when it was announced last year and said he would "still pursue my statutory inquiries". The High Court has now ruled that investigation was outside the scope of the commission's powers.

The High Court battle concerned one of the definitions of "corrupt conduct" in the ICAC Act, which is the source of the commission's investigative powers.

Under the act, conduct of a private citizen that could "adversely affect" the exercise of a public official's functions is one type of corruption. The act says such conduct could involve one of a number of specified criminal offences.

The ICAC has long operated on the basis this definition extends to cases in which a person misleads a public official to bring about a corrupt result.

But the High Court majority rejected this argument and said the public official's probity must be affected.

There was no suggestion Ms Cunneen's alleged conduct – advising her eldest son's girlfriend to feign chest pains to avoid a police breath test after a car crash – resulted in police officers acting dishonestly. Accordingly, the court said this was not "corrupt conduct" the ICAC could investigate.

The ICAC said the majority decision "adopted a construction of [its powers] ... that had never previously been argued or accepted since the ICAC's inception" and had the potential to call into question the prosecutions and convictions of people where the same provision of the ICAC Act was involved.

It would also affect current litigation involving such findings. This would include an appeal by mining mogul Travers Duncan and others against corruption findings made against them following an investigation into a coal tenement at the Obeid family's Bylong Valley farm.

The ICAC said the decision meant the commission "will be unable to investigate or report on several current operations", which had not been revealed, and will "severely restrict" its ability to report on inquiries into Obeid-linked company Australian Water Holdings and Liberal Party fundraising activities.

It urged the government to consider urgent amendments to the ICAC Act that would apply retrospectively, a move supported by the Greens.

A spokesman for Mr Baird said the government was seeking legal advice which would be taken to cabinet. He said all options were still on the table.