Primary legislation may be reviewed to determine its compatibility with European Union (EU) law. Where national law conflicts with any directly effective provision of EU law, the rule of national law must be set aside and EU law applied (R v Secretary of State for Transport, ex parte Factortame Ltd (No 2) [1991] 1 AC 603). As to the reviewability of primary legislation for compatibility with the European Convention on Human Rights in the Human Rights Act 19998, sch. 1, see chapter 88.

Subordinate legislation which has been debated in and approved by affirmative resolution of both Houses of Parliament is susceptible to judicial review (R (Asif Javed) v Secretary of State for the Home Department [2001] EWCA Civ 789, [2002] QB 129).

However, even where there is a private law cause of action, judicial review may still be appropriate where there is a sufficiently public issue. For example, judicial review was appropriate where the question was whether the Secretary of State had exceeded his powers in granting consent to a market of authority to grant leases (R (Corporation of London) v Secretary of State for Environment, Food and Rural Affairs [2004] EWCA Civ 1765, The Times, 27 December 2004, reversed on another point [2006] UKHL 30, [2006] 1 WLR 1721). Similarly, even though declarations can be granted in private law proceedings on the construction of private law contracts without the affected party being a party to the proceedings, where the dispute concerned the construction of a planning agreement under the Town and Country Planning Act 199, s. 106, in reality the document was about the planning objectives of a planning authority, which were therefore public law matters which ought to be dealt with in judicial review proceedings with the local planning authority as a party (Milebush Properties Ltd v Tameside Metropolitan Borough Council [2011] EWCA Civ 270 [2011] PTSR 1654).

The existence of a contractual relationship or a decision based upon the consent of the parties will always make it difficult to establish that the decision is amendable to judicial review (R v Criminal Injuries Compensation Board, ex parte Lain [1967] 2 QB 864; R v National Joint Council for the Craft of Dental Technicians (Dispute Committee), ex parte Neate [1953] 1 QB 704).

However, public law issues may arise where an employer exercises a power which is not wholly contract-based. A decision to suspend a claimant in breach of a code of discipline which had statutory force was reviewable (R v Secretary of State for the Home Department, ex parte Attard (1990) 2 Admin LR 641). The employment conditions of police constables are underpinned by statute and accordingly reviewable (Chief Constable of North Wales Police v Evans [1982] 1 WLR 115). A decision is reviewable if it involves a constitutional or public law principle such as the appointment of Crown prosecutors (R v Crown Prosecution Service, ex parte Hogg (1994) 6 Admin LR 778). Public law issues arise where the question is whether the public body had authority to enter into the contract, but not where the only issue is whether or not there is a breach by a public authority of its own internal procedures or standing orders (as was the case in R v Lambeth London borough Council, ex parte Thompson [1996] COD 217).

Although the courts will not strike out a private law claim simply on the grounds that it would have been more appropriate to use judicial review, they will do so if it amounts to an abuse of process. In deciding whether using a private law claim for a public law issue amounts to an abuse of process the court will consider whether the private law route has been used to take advantage of the longer limitation period, or whether other judicial review rules have been flouted (Clark v University of Lincolnshire and Humberside [2000] 1 WLR 1988). It has been held that where a litigant has a claim which could be brought either by judicial review or by an ordinary action the choice of either might amount to an abuse of process. The exercise of the jurisdiction to strike out the claim on this ground would depend on a consideration of all the relevant circumstances, including any matters occurring before the proceedings were instituted and which remedy would be more appropriate (Phonographic Performance Ltd v Department of Trade and Industry [2004] EWHC 1795 (Ch), [2004] 1 WLR 2893; see also Jones v Powys Local Health Board [2008] EWHC 2562 (Admin), LTL 21/11/2008). For example, proceedings commenced by a landowner seeking declarations in respect of a breach of condition notice in the planning context should have been brought by judicial review since service of a breach of condition notice was a purely public law act, and therefore could not be challenged by private law proceedings (Trim v North Dorset District Council [2010] EWCA Civ 1446, [2011] 1 WLR 1901).