CONCLUSION
[5.59] There are five points that can be made by of way of conclusion on illegality as a ground for review:
i. The ground of illegality requires that decision-makers understand correctly the law that regulates their decision-making power and that they give effect to the law accordingly.
The law, for these purposes, is found not only in statute law, but also in the common law and in EU law and the law of the ECHR (as given effect by the European Communities Act 1972, the European Union Act 2011, and the Human Rights Act 1998).ii. The ground of illegality is not always free-standing, and there can be an overlap in reasoning under the headings of illegality, substantive review, and procedural improÂpriety. There can also be an overlap when EU law and/or the ECHR are in issue.
iii. The common law recognises a category of �constitutional statutes’. These statutes, which are not subject to the ordinary domestic rules on implied repeal, impose a range of obligations on public authorities and, in some instances, on the Northern Ireland Assembly and the Westminster Parliament (albeit subject to the argument that these are self-imposed obligations). The most important such statutes are the European Communities Act 1972, the Human Rights Act 1998, and the Northern Ireland Act 1998 (see [5.04]-[5.33]).
iv. Subordinate legislation can be challenged as contrary to one or other of the conÂstitutional statutes, its parent statute (or related Acts), or the range of common law requirements on illegality. Where the challenge is made with reference to the conÂstitutional statutes, it is important to note that the term â€?subordinate legislation’ does not have a constant meaning and that different considerations may arise depending on context (see [5.34]). Where the challenge is made with reference to the common law it is important to note that, while most of the requirements are of potential application, not all are (see [5.34]-[5.40]).
v. The range of common law requirements that govern the legality of decision-making may be sub-divided into the five headings of relevancy, purposes, bad faith, delegaÂtion, and fettering of discretion (see [5.41]-[5.58]). These headings apply most obviously when decisions or other measures are taken within a statutory framework. The requirements can, however, also found challenges to some exercises of non- statutory power.