National is confident the investigation into Gabriel Makhlouf's Budget hacking claim will prove that Treasury sat on a lie.
The State Services Commissioner Peter Hughes says the investigation will consider the statements made, and the advice the Treasury Secretary provided to the Finance Minister, and his decision to refer the matter to the police.
It has since been revealed that information wasn't hacked and was available through a simple search of the website.
Mr Hughes says it's a matter of considerable public interest and questions need to be answered.
Just before the announcement of the inquiry the Prime Minister was questioned about the controversy and the separate but connected investigation into the unauthorised access to Budget information.
The Prime Minister was then pressed on the timing of Treasury referring the matter to police. Surely the relevant Minister would have been advised before a matter involving the Opposition was referred to police?
Ms Ardern replied she thought the sequence of a ministry making its own decision first, and then advising government ministers, was the only way to remove politics from the decision.