*Editors’ Note: This post is part of the ‘Unwritten Constitutional Norms and Principles Blog Series’*

In 2021 the then Lord Chancellor Robert Buckland QC MP cited the principle of legality as an example of an aspect of public law that might ‘take on a life of [its] own, and lead to the courts overreaching.’ In the simplest terms, the principle of legality is a common law rule of statutory interpretation which mandates that Parliament may only legislate to override constitutional norms using clear language. The principle of legality pertains to statutes alone:  it is not a freestanding principle of the constitution which is applicable to all exercises of public power.

At the turn of the twentieth century, the principle of legality began to be relied upon in a series of judicial review cases involving broad discretionary powers. However, it was the subject of different (yet related) constructions and different (yet related) justifications.

The purpose of this post, however, is not to engage with contemporary debates about the legitimacy of the principle of legality in public law. Instead, it takes a longer view by tracing the historical foundations of legality. Only when we understand legality’s ancestry, can we assess its contemporary impact. Two patterns emerge. First, the ancestry of the ‘principle of legality’ is complex and widespread in the legal system: its historical lineage is not attributable to a single, neat thread of common law doctrine. Unsurprisingly, then, when the principle of legality began to emerge in judicial review cases the 1980s and late 1990s, it manifested in a variety of forms, and was justified according to different assumptions about its constitutional role.

1. Legality’s Complex Ancestry

The precise ancestry of the principle of legality cannot usefully be reduced to a single feature of the common law.  Its roots penetrate the entire legal system. Whilst it is not possible within the confines of this post to trace legality’s ancestry comprehensively, we can usefully illustrate the diversity of ideas which contribute to its modern formulations.  Understanding legality’s ancestry will infuse the contemporary debate about legitimacy with increased rigour.  Legality is derived from two loose categories of rules on statutory interpretation. The first category involves broad interpretive presumptions about statutes, whilst the second is a loose cluster of rules which protect specific common law norms.

Unsurprisingly, various leading works on statutory interpretation reject its novelty. Similarly, Lord Hoffmann explained in Morgan Grenfell [2002] UKHL 21, that the justification for legality ‘is hardly new. It can be traced back at least to Stradling v Morgan (1560) 1 Pl 199. The Stradling case, as interpreted by Lord Bingham in Jackson v Attorney General [2005] UKHL 56 is authority for the proposition that courts ‘will often imply qualifications into the literal meaning of wide and general words [to] prevent them having some unreasonable consequence which Parliament could not have intended.’

Legality is clearly descended from the presumption that statutes are ‘not enacted in a vacuum’ (Cross, Statutory Interpretation (J Bell and G Engle eds, Butterworths, London 1995) 165). This means that ‘[l]ong standing principles of constitutional and administrative law are…assumed by courts to have been taken for granted, by Parliament’ (Cross, Statutory Interpretation, 16). Legality also embodies the presumption against ‘casual change’ in the law. In 1952 Lord Devlin explained that: ‘[i]t is a well-established principle of construction that a statute is not to be taken as effecting a fundamental alteration to the general law unless it uses words that point unmistakably to that conclusion’ (National Assistance Board v Wilkinson [1952] 2 QB 648, 661).

In respect of the second broad category, we can find ample evidence of courts using statutory interpretation to protect specific common law norms. One line of authority concerns the preservation of the courts’ jurisdiction. The Anisminic [1968] UKHL 6 decision is the landmark in the twentieth century, but the jurisprudence is much older. In the eighteenth-century Lord Mansfield made clear in R v Morley (1760) 2 Burr 1040 that Parliament could not preclude the jurisdiction of the courts from supervising the court of Quarter Sessions for legality or want of jurisdiction using ‘general’ words. Removal of the courts’ jurisdiction was possible, but only by using ‘express’ statutory language. Later, in Privacy International [2019] UKSC 22 [100]-[101], Lord Carnwath subsumed similar ideas under the rubric of legality. He explained obiter that ouster clauses could only be achieved using the clearest possible language, but indicated that ‘binding effect cannot be given to a clause which purports wholly to exclude the supervisory jurisdiction of the High Court to review a decision of an inferior court or tribunal, whether for excess or abuse of jurisdiction, or error of law’ [144].

Statutory Interpretation to preserve access to justice also significantly pre-dates the principle of legality. Chapter 40 of the Magna Carta, enacted in 1215, states that ‘[w]e will not sell, or deny, or delay justice to anyone.’ The Supreme Court endorsed Magna Carta as an expression of the constitutional right of access to justice in the twenty-first century (UNISON [2017] UKSC 51 [74]). In UNISON, Lord Reed explained that access to justice was a common law constitutional right, ‘inherent in the rule of law’ [66] andthe Supreme Court held that a fee regime for the employment tribunal was ultra vires due to its adverse impact upon access to justice.

There is also a strong historical presumption that general statutory language will be construed to preserve the liberty of the subject. Magna Carta Chapter 39 mandates that there will be no imprisonment or arrest ‘except by…the law of the land’.  In the seventeenth century, Lord Coke expressed a principle of statutory interpretation in Dr Bonham’s Case (1610) 8 Co. Rep. 107  which foreshadowed the principle of legality. He explained that an Act conferring powers of imprisonment upon the executive ‘shall be taken strictly, or otherwise the liberty of the subject is at their pleasure’.

Property rights are also well established in the common law. The eighteenth-century case of Entick v Carrington (1765) 95 ER 807 is frequently described as a direct ancestor of the principle of legality.  Entick is a yardstick in the English common law’s commitment to the protection of private property and the rule of law. The High Court held that entry into private property to seize papers was unlawful without authorisation by an Act of Parliament.

Statutory interpretation has also been used to prevent the erosion of torts and the principles of criminal law. In Morris v Beardmore [1981] AC 446 the House of Lords held that section 8(2) of the Road Traffic Act 1972 did not authorise a Constable to commit the tort of trespass into a suspect’s property to administer a breathalyser test. This was so because section 8 did not expressly authorise tortious conduct by the police in this context.

In Watkins v Home Office [2006] UKHL 17 [61]Lord Rodger explained that the principle of legality could be traced to the criminal case of Mortensen v Peters (1906) 8 F (J). In Mortensen the House of Lords held that a statute should be interpreted to impose equal liability upon British subjects and foreign nationals. Similarly, in R v Aman Kumar: [2004] EWCA Crim 3207, the Court of Appeal held that pre-existing jurisprudence protecting the principles of criminal law from erosion by general statutory powers could be subsumed within the modern ‘principle of legality’. The Court approved the work of Sir Rupert Cross (cited above,.166). Sir Rupert explained that the presumption that a statute would not displace mens rea without the presence of explicit language was part of a family of presumptions that are ‘of general application and are not dependent on finding an ambiguity in the text.’ (Kumar [19]).

Overall, then, the principle of legality has a complex ancestry. Others would doubtless marshal different cases in support of its heritage. The broader point is, however, that the principle in modern public law is derived from a range of rules on statutory interpretation which aim to protect common law norms from the influence of unclear or generally drafted statutory powers.

2. Legality in Public Law

In view of its complex ancestry, then, it is unsurprising that the principle of legality in contemporary public law has multiple formulations and underlying justifications. In the context of modern administrative law, the foundational principle of legality cases arose in the context of claims about ultra vires administrative action, i.e. claims that the executive had exceeded the scope of powers granted by an Act of Parliament. Yet this does not mean legality cases amount to a simple, or purely functional, exercise in statutory interpretation. Ruling upon the limits of a discretionary statutory power always involves normative choices on the part of the reviewing court. Analysing a statute for compatibility with the principle of legality is no different. By the late 1990s, three different, but connected, justifications for the principle of legality emerged.

The first justification, from Witham [1997] , was that the courts had the common law power to interpret general legislation to prevent the inadvertent erosion of those rights which were ‘logically prior’ to the ‘democratic political process’. The second justification, and the first to adopt the nomenclature of ‘the principle of legality’ appeared in Pierson [1997]. According to Lord Steyn, the principle of legality served to protect the principles of European liberal democracy and the rule of law from attrition by generally worded statutes. Thirdly and finally, the most frequently cited justification comes from Lord Hoffmann in Simms [1999] ). This version of the principle of legality focussed on preventing constitutional norms from being ‘overridden’ by ‘general or ambiguous words’ in legislation. The underlying justification for this was to compensate for the inevitable defects in deliberation that would occur in the Westminster Parliament’s legislative process. Using legality, the courts ‘read down’ or narrow the discretion available to the executive under an Act of Parliament. This has the effect of protecting certain common law norms from the effects of statutory discretion. All the foundational legality cases concern the proper limits of extremely broadly drafted discretionary powers in Acts of Parliament. In respect of the norms protected, four of these foundational cases concern aspects of the right of access to the courts (Raymond v Honey  , Leech  , Witham  and Simms). The remaining case, Pierson , concerned a related norm – the concept that once imposed, a penalty should not be aggravated.

The normative justifications for legality emerged from several judicial review cases in which an Act of Parliament was ‘read down’, or narrowed in its application, to protect the right of access to justice from erosion by the executive. In Raymond the House of Lords held that intercepting correspondence between a prisoner and his solicitor was ultra vires the powers conferred by section 47(1) of the Prisons Act 1952. Lord Wilberforce explained that there was ‘nothing’ in the 1952 Act that authorised any denial or interference with ‘the right of the respondent, as a prisoner, to have unimpeded access to a court.’ Similarly, Lord Bridge agreed it was well established that ‘a citizen’s right to unimpeded access to the courts can only be taken away by express enactment.’ Section 47(1) referred only to the ‘discipline and control’ of prisoners. As such, it was a ‘manifestly insufficient’ legal basis for the Governor’s conduct.

The Court of Appeal decision in Leech also concerned prison rules and legal correspondence. Leech, a prisoner, successfully challenged the practice of censorship of correspondence between prisoners and legal representatives in respect of prospective legal proceedings. Once again, the issue was characterised as ‘simply one of vires’. Steyn LJ read section 47(1) of the 1952 Act as ‘general and unambiguous’ in nature, and endorsed the conclusion in Raymond, above, concerning the constitutional right of access to justice.

Although the above cases demonstrate ‘legality-like’ reasoning, the first case to offer a broad and explicit justification for a non-literal interpretation of statute to protect common law norms was Witham. Witham successfully challenged a fee regime for libel claims, arguing that it was ultra vires because it impeded his right of access to the courts. Laws LJ explained that, notwithstanding the sovereignty of Parliament, certain common law rights could only be abrogated by clear legislative language. This category was limited to rights ‘logically prior’ to ‘the democratic political process’.

In 1997 Lord Steyn made the first explicit reference to the ‘principle of legality’ in Pierson. He expanded the province of legality to include norms apart from rights.  The decision also reoriented the justification for legality towards the broader concepts of the rule of law and liberal democracy. The point of the principle of legality was, in Lord Steyn’s view, a manifestation of deeper substantive values inherent in public law. Legality was justified because:

Parliament legislates for a European liberal democracy founded on the principles and traditions of the common law

Specifically, ‘the rule of law enforces minimum standards of fairness, both substantive and procedural.’ These commitments meant that: ‘[u]nless there is the clearest provision to the contrary, Parliament must be presumed not to legislate contrary to the rule of law’.

The final, and most cited version of the principle of legality was articulated in 1999 by Lord Hoffmann in Simms. This vision of legality, unlike the others, was activated not only by general statutory language, but by provisions which were ‘general or ambiguous’ (emphasis added).Lord Hoffmann’s conception of legality is underpinned by distinct, but related, ideas from the previous cases.  In contrast with Lord Steyn, Lord Hoffmann did not ground the justification for legality in either an explicitly substantive vision of the rule of law or in liberal democracy. Instead, his justification for legality encompassed a deeper vision of how the legislative and wider democratic processes both legitimised Parliament’s legislative supremacy yet compensated for its inevitable oversights.

He explained that Parliament’s ability to override fundamental rights or constitutional norms was legitimated by the fact that it must ‘squarely confront’ any ‘political cost’ resulting from such a choice. This vision of legality rests upon assumptions about the good health of the wider constitutional and democratic culture. It also assumes a broader commitment to the values which legality protects by parliamentarians and the electorate. Secondly, this principle of legality apparently constitutes a failsafe for potential shortcomings in the Westminster legislative process. Lord Hoffmann’s suggestion that it is necessary to interpret legislation in conformity with fundamental rights and principles is compelled by his conclusion that there is ‘too great a risk that the full implications of their unqualified meaning may have passed unnoticed in the democratic process.’ Finally, this meant that legality requires the courts to continue to acknowledge parliamentary sovereignty whilst applying ‘principles of constitutionality little different from those…countries where the power of the legislature is expressly limited by a constitutional document.’

Within the three conceptions of, and justifications for, the principle, much is left unsaid, and many questions are raised. For example, in Witham, the nature of the rights which are logically prior to the democratic process are never articulated. Nor do we know precisely what the values of a ‘European Liberal Democracy’ that might be brought to bear on the interpretation of general statutory language might be (Pierson). Finally, it is not clear how, if at all, a reviewing court is to assess whether a legislative process has been appropriately attentive to fundamental constitutional norms (Simms). Like many legal concepts, the edges are fuzzy, and the rationale contestable. But we should not be tempted to let perfection be the enemy of the good.

3. Conclusion

Despite all the latitude and ambiguity inherent in each vision of the principle of legality, its use in modern public law clearly embodies a distillation of many deeply embedded historical facets of the common law. It is therefore unsurprising that history drives courts to different conceptions and justifications of the principle of legality.

There is ample evidence to suggest, there is nothing novel about a principle of judicial interpretation which seeks to prevent ‘general’ or ‘ambiguous’ statutory language from overturning well-established common law norms in a public law context. Yet, it is also clear that recourse to the principle of legality is not a value neutral exercise. Legislation which is clear upon its face is subjected to judicial interpretation underpinned by a range of values and justifications to determine its vires. Despite the depth of legality’s historical roots, there is no singular agreed methodology for determining which values take priority. In the context of broad discretionary powers enacted to enable the execution of public administration, recourse to the principle of legality in specific circumstances may generate controversial outcomes. Equally, judicial refusals to invoke the principle of legality may also prove controversial (R (Project for Registration of British Citizens v Home Secretary [2022] UKSC 3)

Moreover, different judicially articulated visions of law and politics undergird judicial recourse to the ‘principle of legality’. Yet in Leech, Simms, and Pierson, a breach of the ‘principle of legality’ was one of several approaches to classifying the legal error alleged. Other judges reach the same result using more established grounds of review. What then, might the principle of legality add to public law? One possible answer is that legality, in all its incarnations, acts as a ‘mediating’ device which allows a court to openly protect specific norms inherent in the common law constitution. What legality adds, then, is a degree of transparency about what the common law constitution values, that is not readily captured by other grounds of review.

Thanks to Se-Shauna Wheatle, Vanessa MacDonnell and Mike Gordon for helpful editorial suggestions. All errors and omissions are the author’s.

Hayley J. Hooper, Associate Professor, University of Oxford

Hayley is currently authoring a book on ‘The Principle of Legality’ as part of the Hart: Bloomsbury Key Ideas in Law series.

(Suggested citation: H. J. Hooper, ‘Historical Origins of the ‘Principle of Legality’ in British Public Law’, U.K. Const. L. Blog (20th May 2024) (available at https://ukconstitutionallaw.org/)