1. “Ultra vires” or excess of jurisdiction
Decision-makers only have the power to make decisions within the boundaries set down by the law. When a decision is made in excess of such boundaries, it is liable to be set aside by a Court. See for example Wong Kam Kuen v The Commissioner for Television and Entertainment Licensing [2003] 3 HKLRD 596 where the court set aside the decision made by the Commissioner for Television and Entertainment Licensing on obscenity and indecency on the ground that such decision belonged (in law) to the power of the Obscene Articles Tribunal.
While certain incidental powers may be granted in order to allow a decision-maker to exercise the powers expressly provided for under the law, they will only be given in cases where reasonably necessary (see for example section 40 of the Interpretation and General Clauses Ordinance (Cap. 1)). Provision of powers for mere convenience or desirability are not valid reasons.