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

Unwritten constitutional principles supply much of the foundation – or ‘hidden wiring’ – of the UK constitution. As Lord Reed has recently recognised, the constitution relies on numerous ‘understandings, generally tacit, about how power should be exercised’. Constitutional form and constitutional culture, working in combination, have produced a state in which even vital constitutional principles remain somewhat elusive; Lord Reed continues: ‘[b]ecause we have no written constitution, and court cases raising constitutional questions have until recently been few and far between, there has been relatively little by way of legal definition of constitutional principles.’ Nonetheless, courts and political organs recognise the role of the rule of law, parliamentary sovereignty, and separation of powers as animating principles of the constitution. These principles sit alongside – and to varying degrees are reflected in – the numerous constitutional conventions that primarily condition the powers and activities of political actors. While at first glance there may appear to be a clear demarcation between political and legal norms, many unwritten constitutional norms and principles have both political and legal dimensions, with the corollary that there are multiple avenues for their normative development and enforcement. In fact, principles that are often recognised and utilized as legal constitutional principles are invoked in parliamentary scrutiny, executive decision-making and political debate. Meanwhile there are intimations of courts engaging with norms of political conduct by adjudicating on related or intertwined constitutional principles or reasoning by reference to the legal dimensions of political norms. The interrelationships between the legal and political dimensions of unwritten constitutional norms is therefore a topic which is ripe with potential.

Constitutional principles and conventions undoubtedly share core features. Chief among these is that their normative force and content are not (wholly) derived from representations in written texts. Accordingly, though the rule of law is referenced in the Constitutional Reform Act 2005 and parliamentary sovereignty acknowledged in both the European Union (Withdrawal Agreement) Act 2020 and the Safety of Rwanda (Asylum and Immigration) Act 2024, the relevant provisions do not capture – or even attempt to explain – the meaning or effects of the respective principle. The normative value of the constitutional principle is not, in the examples given, founded on – or perhaps even furthered by – the statute. Indeed, the references in each statute instead reflect an extant state: s.1(1) of the Constitutional Reform Act speaks of the rule of law as an ‘existing constitutional principle’; s.38 of the European Union (Withdrawal Agreement) Act 2020 and s.1(4)(a) of the Safety of Rwanda (Asylum and Immigration) Act 2024 ‘recognise’ the sovereignty of the UK Parliament. Similar can be said of codified conventions; while the Ministerial Code outlines much of the content of the convention of individual ministerial responsibility, the convention itself predates publication of the Code (and indeed its predecessor document, Questions of Procedure for Ministers) and the content and authority of the convention exist beyond the confines of its modern, ‘codified’, variant.

Unwritten constitutional principles and conventions are also associated with high degrees of flexibility. While it would be an overstatement to claim that flexibility is a feature of all conventions, many – including those that shape the everyday work of Parliament and the government – are open to evolution in response to changing political climate and morality. Principles, meanwhile, are flexible in that they can be observed and respected – as well as undermined – by degrees. Thus, as Dworkin explains, while rules generally apply in an all or nothing fashion, a principle may be infringed to a degree and yet maintain its validity. In consequence, there may also be legitimate variation in perceptions of the requirements of a particular principle. At the minimalist end of the spectrum, the rule of law – for instance – might be argued to stand only for the base principle of government in accordance with law; maximalist understandings of the rule of law, by contrast, view the principle as providing the meta framework for a just legal system.

Dual Dimensions

The rule of law is primarily conceived as a legal principle, which courts are responsible for describing and enforcing. In Privacy International Lord Carnwath went so far as to claim that ‘there is nothing controversial in the proposition that it is for the courts, and ultimately the Supreme Court … to determine its content and limits’ [para 121] and ‘it is ultimately for the courts, not the legislature, to determine the limits set by the rule of law to the power to exclude review’ [para 131]. However, the rule of law is also a principle of ‘political morality’ and the orthodox procedural requirements of even thin accounts of the rule of law speak to both legal and political actions and behaviours. The Ministerial Code, for instance, clearly reflects a core rule of law value when it speaks of Ministers’ ‘overarching duty … to comply with the law’ [para 1.3]. Similar stipulations can be found in the Cabinet Manual, and (in relation to the permanent staff of government) the Civil Service Code.

Further, observation of political actors reveals that the political branches also play a role in both determining the content and the boundaries of the rule of law. Several parliamentary committees – such as the House of Lords’ Constitution Committee, International Agreements Committee and Delegated Powers and Regulatory Reform Committee, and the Joint Committee on Human Rights, reason by reference to constitutional principles such as the separation of powers and the rule of law in undertaking their legislative and scrutiny functions. The records of the Constitution Committee, in particular, are instructive as – since its establishment in 2001 – the Committee ‘has adopted a number of clear and consistent positions on the meaning of certain constitutional norms in the legislative context’, including the rule of law and the separation of powers. On this basis, the Constitution Unit at UCL has published, and updated across three editions, a report ‘codifying’ The Constitutional Standards of the House of Lords Select Committee on the Constitution, with the authors recognising that the Committee ‘has demonstrated the relevance of the normative content of the constitution to the legislative process.’

Meanwhile, ostensibly political norms – including constitutional conventions that regulate governmental and monarchical powers – are recognised and (indirectly) endorsed by courts. A salient example can be found in R (Evans) v Attorney General, in which the Supreme Court recognised conventions relating to relations between the monarch and government (including ‘the ability of the Sovereign to … consult, to encourage and to warn’ (the ‘tripartite’ convention) and the right of the heir to the throne to be ‘instructed in the business of government’ (the ‘education’ convention). In parallel with the statutory recognition of constitutional principles, such ‘recognition’ adds weight to the suggestion that the convention in question ought to be regarded – including by constitutional actors to whom it does not apply – as carrying regulatory weight. While such recognition may not – as evidenced in Miller 1’s treatment of the Sewel convention – result in any material change to the locus of enforceability for the political norm, judicial notice of a convention may nonetheless serve as a valuable indicator of a broad consensus as to its existence and (potentially) its scope. Judicial consideration of political norms, such as that found in the Upper Tribunal decision in Evans v Information Commissioner, can also operate to support the concretisation of constitutional standards that may be infrequently articulated, providing a reinforcing form of quasi-codification.

More recently, the recognition in R (FDA) v Prime Minister that parts of the Ministerial Code may be justiciable underscores that the line between political and legal norms is flexible and changeable and that accountability for compliance with these standards may in some circumstances be exercised by legal as well as political actors. The FDA trade union contended that the PM misdirected himself in deciding that the Home Secretary had not breached the Ministerial Code despite the Independent Adviser on Minister’s Interests finding that the minister engaged in bullying and thereby breached the Code. The Divisional Court found the claim justiciable despite ultimately finding that the Prime Minister had not misdirected himself. The finding on justiciability follows in the footsteps of the Court of Appeal’s consideration in the Gulf Centre case of a challenge to the deletion of a ministerial duty to comply with international law in the Ministerial Code in preference for a general ‘duty to comply with the law’. The Divisional Court’s reasoning in FDA provides indications of factors that influence whether a norm will be seen as justiciable. Firstly, the subject matter, not the source of the norm, is determinative. Second, whether the subject matter in the Ministerial Code is suitable for judicial determination was said to rest on ‘constitutional competence’ [legitimacy] and institutional capability, and that the courts’ ability to intervene would be limited ‘where [the] issues in dispute are not ones suitable, or capable, of being resolved by a court as part of legal proceedings’ [para 34]. The court therefore pointed to the ability of judges to provide definitions of the terms “harassment”, “bullying” and “discriminating behaviour” in the Ministerial Code. The FDA decision and the circumstances that gave rise to it demonstrate coterminous and interlocking legal and political standards.

Mapping the Nexus between Legal and Political Unwritten Constitutional Norms and Principles

There are several ways to conceive and frame the nexus between political and legal unwritten constitutional norms and principles. We propose four conceptions, but these conceptions are not necessarily exhaustive, and their boundaries are somewhat permeable. First, a principle may be directly enforceable in only one or the other of the legal or political spheres, but both legal and political organs recognise and take cognisance of the principle. This traditional and constitutionally conservative formulation is represented in Miller I’s resounding rejection of a claim to enforce the Sewel Convention with the Supreme Court’s firm rejoinder that ‘judges … are neither the parents nor guardians of conventions; they are merely observers’ [at para 146].

Second, legal principles and political norms can be perceived as sharing common moral imperatives or normative foundations. The convention that politicians should not criticise individual judges and the legal principle of judicial independence both share a common imperative of protecting the freedom of the judiciary to make decisions on the merits of cases. This freedom is an essential component of fairness in decision-making and of the rule of law.

Third, a general principle may be seen as giving rise to rules and norms, some of which are applicable in the legal space and some of which are applicable in the political sphere. The principle of parliamentary supremacy provides an example of this dynamic. The principle gives rise to the conventions that the government only maintains its authority through the continued confidence of the House of Commons and that ministers are accountable to Parliament for actions and decisions within their ministerial brief. It also gives rise to the legal rule that Acts of Parliament are superior to judicial decisions, so for instance, an Act of Parliament can overrule or undermine the effect of judicial decision as recently, and controversially, illustrated by the effective override of the Supreme Court’s decision in R (AAA) v Secretary of State for the Home Department in the Safety of Rwanda (Asylum and Immigration) Act 2024. The principle also, of course, underpins the general rule that if two statutes are inconsistent, the earlier statute is judged to be impliedly repealed by the more recent enactment.

Fourth, a principle may be applicable in both legal and political spaces within the constitution, but enforceable in different ways by political and legal organs, according to the branches’ respective institutional processes and limitations. This conceptualisation offers an explanatory framework for the Supreme Court’s Miller II; Cherry decision that the 5-week prorogation of Parliament by PM Boris Johnson unlawfully undermined parliamentary accountability and therefore parliamentary supremacy. Though the Court was accused in some quarters of converting a political norm – parliamentary accountability – into a legal principle, a more realistic understanding of the consequences of the decision is to view the accountability principle as one that sounds in both the legal and political spheres, but is subject to distinct enforcement mechanisms.

The first conception is too conservative and restrictive in our view. It presents an impoverished view of the principles and norms that animate the constitution. Moreover, it rests on a mistaken view that there are hard lines between unwritten constitutional principles and the conventional/political norms that often evidence their practical purchase. Indeed, the duality of the nature and application or unwritten constitutional norms and principles underpins much of their utility in both constitution building and constitutional accountability. As we have sought to argue elsewhere, for instance, separation of powers remains a useful tool of constitutional argumentation in the UK even though its requirements may be contestable and (generally) lack legal enforceability. Beyond a rejection of the first conception, however, we express no firm preference for any of the remaining conceptions. This restraint is exercised for several reasons. First, these categories are not mutually exclusive. For instance, the second category of shared moral imperatives can be adopted alongside the remaining categories. An unwritten constitutional principle and constitutional convention can be founded on a common moral or societal imperative while simultaneously being based on a general principle that gives rise to both legal rules and political norms. In this sense, the distinction between the categories depends in some circumstance on the level of abstraction. The second reason for restraint is that the ‘accurate’ or most convincing framing may depend on the jurisdiction in question and that jurisdiction’s distribution of constitutional norms and power. Though our discussion has focused on the UK, the position may therefore be different in, for instance, Canada with its codified constitution which transitioned Canada from parliamentary to constitutional supremacy. (See analyses of constitutional law and conventions and unwritten constitutional principles and conventions by Macfarlane (2022) and MacDonnell and Lagassé (2023).) Identifying the extent to which factors depend on domestic constitutional architecture and power distribution – as opposed to general Westminster design – will necessarily contribute to more accurate depictions of the legal and political dimensions of the unwritten norms and principles of the UK’s constitution.

Conclusion: Problematising the Dual Dimensions of Unwritten Constitutional Norms and Principles

The coexistence of legal and political facets of unwritten constitutional norms and principles may be a double-edged sword, especially when there is judicial enforcement of constitutional norms which are ostensibly, or traditionally conceived as, ‘political’. Such cases engender consternation about two traditional dividing lines in UK constitutionalism: the line between judicial and parliamentary power and the line between (justiciable) legal and (non-justiciable) political issues. Specifically, such decisions trigger accusations of judicial encroachment on the political sphere, the conversion of political issues into legal issues and, ultimately, the domination of political accountability by legal regulation. While the ideas in this blog post do not prioritise questions of the desirability or legitimacy of judicial enforcement of political norms, the analysis undertaken here suggests that hard and fast divisions – while nominally appealing for their simplicity – cannot provide an adequate, or accurate, picture of the complex interrelationships between constitutional principles and their political and legal relations.

Thanks to Hayley Hooper, Vanessa MacDonnell and Paul Scott for their helpful feedback.

Se-shauna Wheatle is Associate Professor in Law at Durham Law School

Roger Masterman is Professor of Law at Durham Law School

(Suggested citation: S. Wheatle and R. Masterman: ‘The Legal and Political Dimensions of Unwritten Constitutional Norms and Principles’, U.K. Const. L. Blog (29th May 2024) (available at https://ukconstitutionallaw.org/)