The Cunneen ruling gave a narrower interpretation to ICAC's powers than the watchdog had believed applied, and cast doubt on its ability to make findings against Mr Duncan and others. The retrospective laws validated those findings. Since the Cunneen ruling, an expert panel appointed by the Baird government and headed by former High Court chief justice Murray Gleeson and Sydney silk Bruce McClintock has recommended changes to the ICAC Act which restore the bulk of those powers in future inquiries. Laws were introduced in Parliament on Tuesday to implement the recommendations. Mr Duncan's legal team had argued the retrospective laws were invalid because they usurped the judicial power given to courts under the Constitution. They said the laws were an "impermissible command or direction" to the courts not to overturn findings against Mr Duncan and others in accordance with the Cunneen decision. But in a joint judgment, Chief Justice Robert French and Justices Susan Kiefel, Virginia Bell and Patrick Keane said Mr Duncan's lawyers had advanced an interpretation of the laws that was "distinctly implausible". "It is now well settled that a statute which alters substantive rights does not involve an interference with judicial power ... even if those rights are in issue in pending litigation," the judgment said.

In a separate judgment, Justice Stephen Gageler said the constitutional argument advanced by Mr Duncan's lawyers "teeters on a narrow proposition of statutory construction" that was incorrect. Justices Geoffrey Nettle and Michelle Gordon said in a joint judgment that the laws simply created a "new or different legal regime" and did not overstep Parliament's powers. Mr Duncan and three of his business associates – John McGuigan, John Atkinson and Richard Poole – were found to have acted corruptly by concealing the Obeid family's interest in a coal tenement from authorities. The men are likely to challenge the findings on different legal grounds in the Court of Appeal. The High Court ruling removes one legal obstacle to ICAC delivering reports in its high-profile inquiries into Liberal Party fundraising and infrastructure company Australian Water Holdings, which had links to both sides of politics including the Obeid family. Under the High Court ruling in Cunneen, parts of those inquiries would have been outside the scope of ICAC's jurisdiction.

But the court has yet to deliver its ruling in another legal challenge brought by property developer and former Newcastle mayor Jeff McCloy, who is seeking to have NSW laws banning political donations from developers struck down on the basis they infringe the implied freedom of political communication in the constitution. Mr McCloy became famous for his largesse when admitted at ICAC last year to giving envelopes containing $10,000 in cash to state Liberal candidates before the 2011 election, in breach of the developer donations ban. If the ban is overturned by the High Court, Mr McCloy would not have broken the law and ICAC's ability to make findings in major parts of that investigation will be thrown into doubt. Greens MP Jamie Parker, the party's anti-corruption spokesman, said the decision "marks an important step in the effort to ensure that NSW has robust laws to fight corruption". He said Premier Mike Baird should be "emboldened" by the decision and introduce new statutory offences relating to misconduct in public office. This was one of the recommendations of a parliamentary committee on ICAC and is supported by the corruption watchdog.



"Codifying common law offences such as misconduct in public office and bribery will facilitate prosecutions arising from ICAC investigations," Mr Parker said.



"By codifying these offences, NSW will finally come into line with the Commonwealth and other states which have introduced statutory offences in these areas."