The rule of law

The rule of law stands alongside parliamentary sovereignty as a foundational principle of the United Kingdom constitution. It denotes, in its most basic sense, the idea that law — not arbitrary power — governs society. Yet that seemingly uncontroversial statement masks profound disagreement about the principle's content, scope, and justiciability. Does the rule of law require merely that rules be clear, prospective, and publicly promulgated? Or does it impose substantive constraints on what rules Parliament may enact — protecting, for instance, fundamental rights or access to justice?

This note traces the competing conceptions of the rule of law from Dicey's Introduction to the Study of the Law of the Constitution (1885) through to Lord Bingham's modern synthesis and beyond. We examine the formal or 'thin' theory associated with Joseph Raz, the substantive or 'thick' theory articulated by Ronald Dworkin and endorsed (in modified form) by Tom Bingham, and the common law constitutionalism advanced by Trevor Allan and Sir John Laws. The tension between these theories has profound practical consequences: it determines whether courts may disapply or interpret legislation to vindicate rule-of-law values, and whether emergency powers, ouster clauses, or retrospective taxation can survive judicial scrutiny.

After completing Week 2 on parliamentary sovereignty, you will already appreciate that any robust rule-of-law principle may collide with legislative supremacy. This week explores precisely that collision. We consider landmark judgments — Entick v Carrington, M v Home Office, Pierson, Anisminic, Privacy International, Miller (No 1), Unison — in which courts have invoked the rule of law to control executive discretion, protect access to justice, and occasionally hint at limits on Parliament itself. We also examine key statutory interventions: the Constitutional Reform Act 2005 (which placed both rule of law and judicial independence on a statutory footing) and the Constitutional Reform and Governance Act 2010 (which codified civil service impartiality).

Academic debate remains intense. Scholars such as Paul Craig, Trevor Allan, Jeffrey Jowell, and Sir Stephen Sedley defend varying degrees of substantive content; Richard Ekins and John Finnis warn that thick conceptions undermine democracy and legal certainty. For Mods candidates, mastery of these positions — and the ability to deploy them in argument — is essential. The note concludes with a full worked essay, five graded practice questions, and a guide to common exam traps.

This note assumes familiarity with parliamentary sovereignty and the dualist sources of UK constitutional law covered in Weeks 1 and 2.

Although the phrase 'rule of law' became current only in the nineteenth century, its intellectual lineage reaches back to classical antiquity. Aristotle distinguished the rule of law from the rule of men; the Roman jurist Cicero extolled lex over imperium. Bracton's thirteenth-century dictum — that the king is under God and the law — encapsulates medieval English resistance to absolute monarchy, a theme echoed in Magna Carta 1215 (particularly clause 39, protecting freemen from imprisonment or dispossession save by lawful judgment) and the Petition of Right 1628.

The Glorious Revolution settlement of 1688–89 entrenched parliamentary supremacy, but it also affirmed the illegality of suspending or dispensing with law by royal prerogative (Bill of Rights 1689, Art 1). Locke's Second Treatise of Government (1689) argued that legitimate authority derives from consent and must operate through standing, promulgated laws. Montesquieu's De l'esprit des lois (1748) emphasized separation of powers and the independence of judges as safeguards against tyranny. By the late eighteenth century, English judges were vindicating liberty through the common law: Entick v Carrington (1765) held that executive officers could not lawfully search premises without statutory or common law authority. Lord Camden CJ's judgment — 'if it is law, it will be found in our books' — remains an iconic statement that power must be justified by law.

A.V. Dicey synthesized these strands in his Introduction to the Study of the Law of the Constitution (1885). Writing against the backdrop of continental droit administratif and Austinian positivism, Dicey identified three meanings of the rule of law: (1) the absence of arbitrary power and the supremacy of regular law; (2) equality before the law; and (3) the predominance of the common law and ordinary courts in protecting constitutional rights, rather than a separate code of public law. Dicey's account was both descriptive and prescriptive. He admired English liberty and distrusted administrative discretion. Yet his formulation was problematic: his hostility to discretion sat uneasily with the growth of the regulatory state; his equation of rule of law with parliamentary sovereignty left no space for judicial review of legislation; and his contrast with French droit administratif rested on a misunderstanding of the Conseil d'État.

By the mid-twentieth century, executive power had expanded dramatically. The rise of delegated legislation, emergency powers, and the administrative state posed fresh challenges. Hayek's The Road to Serfdom (1944) and The Constitution of Liberty (1960) revived liberal concern about discretion and central planning. The post-war emergence of international human rights law — the European Convention on Human Rights 1950, the International Covenant on Civil and Political Rights 1966 — placed rule-of-law protections in a transnational frame. In the United Kingdom, the growth of judicial review from the 1960s onwards saw courts develop common law principles — fairness, rationality, legality — that constrained executive action. Lord Diplock's tripartite classification in GCHQ (1985) and Lord Bingham's eight principles in The Rule of Law (2010) represent modern attempts to articulate the doctrine's content in a way responsive to contemporary governance.

Thin versus thick conceptions

The central cleavage in rule-of-law theory is between formal (thin) and substantive (thick) conceptions. Formal theories — most influentially propounded by Joseph Raz — hold that the rule of law is concerned with the manner in which law is made and administered, not its content. Raz identifies eight requirements: laws should be prospective, open, and clear; relatively stable; particular laws (such as bye-laws) should be guided by general rules; the independence of the judiciary must be guaranteed; the principles of natural justice must be observed; courts should have powers of review over legislative and administrative action; courts should be accessible; and the discretion of crime-preventing agencies should not be allowed to pervert the law.

On this view, the rule of law is a procedural or instrumental virtue. An unjust law can still comply with rule-of-law standards if it is clear, prospective, and applied impartially. The rule of law says nothing about whether detention without trial, racial discrimination, or retrospective penalties are wrong — only that if such measures are enacted, they must satisfy formal criteria. Raz's account has the virtue of clarity and avoids collapsing rule of law into a general theory of political morality. It respects the positivist distinction between law and morality and is compatible with parliamentary sovereignty: Parliament may enact any content, provided it follows proper form.

Entick v Carrington (1765): legality and executive power

Lord Camden CJ's judgment in Entick v Carrington is the foundational statement that executive action requires legal justification. The Secretary of State had issued a warrant authorizing messengers to search Entick's premises and seize his papers. The Court of Common Pleas held the warrant unlawful: neither statute nor common law authorized such a power, and the defendant could point to no precedent. 'If it is law, it will be found in our books. If it is not to be found there, it is not law.' The case establishes the principle of legality: government cannot act without lawful authority. It prefigures modern judicial review and remains regularly cited.

M v Home Office [1994] 1 AC 377: rule of law and Crown immunity

This House of Lords decision affirmed that ministers and the Crown are subject to the law and that courts may grant coercive remedies (contempt of court, injunctions) against ministers acting in their official capacity. M, an asylum-seeker, sought judicial review; the judge initially granted interim relief, but the Home Secretary deported him in breach of undertakings. The Court of Appeal found the Home Secretary in contempt. The House of Lords upheld that finding (though setting aside the contempt order on procedural grounds). Lord Templeman stated that the rule of law requires that ministers and civil servants be subject to law, and that courts must have effective remedies to vindicate rights. The case rejected residual Crown immunity in public law, marking a decisive shift from prerogative to legal accountability.

R v Secretary of State for the Home Department, ex p Pierson [1998] AC 539: substantive legitimate expectations and the principle of legality

Pierson involved the Home Secretary's retrospective increase of a mandatory lifer's tariff. The House of Lords held that the Secretary's policy was unlawful because it violated a substantive legitimate expectation and the principle that powers must not be exercised to increase punishment retrospectively. Lord Browne-Wilkinson and Lord Steyn both emphasized rule-of-law values: retrospective increases in punishment offend legal certainty and proportionality. Lord Steyn articulated the principle of legality: Parliament must squarely confront what it is doing and accept the political cost if it wishes to override fundamental rights. Ambiguous or general words will not suffice. Pierson is a leading authority for the proposition that the rule of law generates interpretive principles constraining statutory discretion.

R (Unison) v Lord Chancellor [2017] UKSC 51: access to justice

The Supreme Court unanimously held that the Lord Chancellor's fees order for employment tribunals was unlawful. The fees were so high as effectively to prevent access to justice, violating both common law and EU law principles. Lord Reed delivered a magisterial judgment on the constitutional importance of access to justice. He held that the right of access to courts is inherent in the rule of law and cannot be abrogated by the executive without clear statutory authority. Even where statute confers power to impose fees, that power must be exercised compatibly with the constitutional right of access. Unison is now the leading authority on access to justice and demonstrates the courts' willingness to strike down subordinate legislation that undermines rule-of-law fundamentals.

R (Privacy International) v Investigatory Powers Tribunal [2019] UKSC 22: ouster clauses and judicial review

Privacy International concerned an ouster clause in the Regulation of Investigatory Powers Act 2000, s 67(8), purporting to exclude judicial review of decisions of the Investigatory Powers Tribunal. A majority of the Supreme Court (Lord Carnwath, Lord Lloyd-Jones, Lady Black, Lord Kerr, and Lady Hale) held that even a strongly worded ouster clause could not exclude review for jurisdictional error. To oust review entirely would require the 'most clear and explicit words' (Lord Carnwath at [144]). Lord Carnwath invoked the rule of law and the Constitutional Reform Act 2005, s 1, concluding that the supervisory jurisdiction of the High Court — rooted in the common law — cannot be ousted by inference or general words. Lords Sumption, Reed, and Wilson, while concurring in the result on other grounds, took a narrower view, emphasizing parliamentary sovereignty. Privacy International is central to debates about the limits of Parliament's power to exclude judicial scrutiny.

R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5: prerogative and statute

In Miller (No 1), the Supreme Court held that the Crown could not trigger Article 50 TEU (initiating Brexit) by prerogative alone; an Act of Parliament was required. The Court reasoned that triggering Article 50 would inevitably result in changes to domestic law — the loss of EU-derived rights — and the prerogative cannot be used to alter domestic law. The judgment reaffirms the principle of legality: major changes to legal rights require statutory authority. While the case is often discussed under parliamentary sovereignty and prerogative, it also illustrates rule-of-law reasoning: legal certainty, authorization by law, and the subordination of executive to legislative will.

See practice questions below.

See further reading below.