There are a number of different grounds for challenging a decision.

A court will interfere with an administrative decision or question if it can be shown to go beyond the powers given to the decision maker by Parliament. An administrative action that goes beyond this power is called ultra vires. There is a great deal of case law on the various reasons why a decision may be ultra vires. These are summarised in the following paragraphs.

Irrelevant Considerations - This is the most important ultra vires ground. If it can be shown that a government body, in reaching its conclusions, took into account factors that were not relevant to the matter, or failed to consider matters that were relevant, the court can intervene. In order to decide what is relevant it is necessary to compare the reasons given for the dcision or action with those permitted by the Act.

Improper Purpose - This is probably the second most common ultra vires ground. Often, the same factual situation will justify court action on the basis of both irrelevant consideration and improper purpose. Strictly speaking, the claim here is that the decision or action, although on its face proper under the law, is designed to achieve a purpose which is beyond the responsibilities of the government body.

Unreasonableness - A much less readily available ground is to claim that a decision is so unreasonable that no reasonable body would have reached it. This is a difficult ground, because it admits initially that the decision was one that was permissible under the law. What the individual is contending is that it is so unreasonable an application of the law that it goes beyond the inferred limits of the power. Generally speaking, the courts are not inclined to replace their view of hat might be reasonable for that of an outside body, especially an elected body such as a local council.

Bad Faith - To attack an administrative action on the ground of bad faith it is necessary to show that the decision was affected by corruption, bribery or similar malpractice.

Uncertainty - A ground which is rarely available for attacking an administrative action is that it was too uncertain to be meaningful.

No Evidence - This is a relatively recent development in the review of administrative action, as the courts are more prepared now than previously to review decisions where the evidence does not appear reasonably capable of supporting the decision made.

Beyond Jurisdiction - A decision that affects the rights or interests of an individual can be challenged on the grounds that it is beyond the jurisdiction of the decision making body.

Error of Law - Normally, tribunals are free to make legal principles in the field in which they are concerned, but sometimes the law has been decided in other decisions. The tribunal must follow these established principles.

It is sometimes possible to attack a tribunal's decision on the basis that it is obvious from the record of its proceedings or the reason for its decision that it misunderstood some established principle. This is known as an error of law on the face of the record.