INTRODUCTION

[4.01] The purpose of this chapter is to identify the public law precepts that underpin the grounds of illegality, substantive review, and procedural impropriety that may be argued in an application for judicial review.^[666] The grounds, which determine how closely and for which reasons the courts will scrutinise public law decisions and so on,^[667] cor­respond to debates about the constitutional role of the courts and the relevance of doctrines such as the separation of powers.^[668] Judicial review in Northern Ireland and elsewhere in the UK was previously synonymous with a �review, not appeal’ distinction that entails that the courts do not take substantive decisions in the place of bodies that the legislature has entrusted with a particular statutory function.^[669] However, while the courts often emphasise that the imperative of judicial self-restraint remains,^[670] they have also modified the grounds for judicial review—whether with reference to the common law and/or to EU law and the ECHR^[671]—to permit closer look review where the context of a case is taken to require such review (judicial review is now also available for purposes of challenging various forms of non-statutory power—see [4.06]-[4.08]^[672]). In identifying the precepts that underlie these variable and context-sensitive grounds for review this chapter thus examines: the constitutional purposes of, and limits to, the grounds; the approach of the courts to statutory powers, duties, and discretion (an issue which is central to the workings of the separation of powers doctrine); and the approach of the courts to errors of law and errors of fact on the part of subordinate decision-makers.

[4.02] One further point by way of introduction concerns the overlapping nature of the grounds for judicial review. Although the grounds may be listed as illegality, sub­stantive review and procedural impropriety (principles such as proportionality, legitimate expectation, and so on, then exist within those), a decision that is challengeable under one heading will often also be challengeable under another.^[673] The case law considered in this chapter should therefore not be read as of relevance to only one or other of the grounds, but rather as of more general importance to developments in judicial review.