Failure to comply with Lord Greene's well-worn directive may render a decision ultra vires for failure to take into account a relevant consideration. Conversely, if there are matters to which a decision maker clearly should not have regard, a decision may be ultra vires for taking into account an irrelevant consideration, if such factors are indeed taken into account.

This ground, or perhaps more accurately grounds, of judicial review are enshrined in both common law and statute. The Commonwealth Administrative Decisions (Judicial Review) Act 1977 states in s5(2) that an improper exercise of discretion includes (a) taking an irrelevant consideration into account in the exercise of power and (b) failing to take a relevant consideration into account in the exercise of power. Their history, however, has not been spectacular. From the Wednesbury case through to foundational Australian cases such as Minister for Aboriginal Affairs v Peko-Wallsend Ltd and Sean Investments Pty Ltd v MacKellar, courts have presented the task of judicial review of an administrative decision on the considerations ground as a simple and straightforward exercise in statutory interpretation. Parliament confers discretionary power on a decision maker, the limits of which can be simply ascertained from a reading of the relevant legislation.