Sources and nature of the UK constitution

The United Kingdom constitution occupies a singular position among modern liberal democracies. It is uncodified, lacking a single, entrenched foundational document analogous to the Constitution of the United States or the Grundgesetz of Germany. This does not mean that the UK lacks a constitution. Rather, the constitution is to be found in a heterogeneous collection of sources—statute, common law, convention, works of authority, and the law and custom of Parliament—which together establish the organs of state, regulate the relationships between them, and protect the rights of the individual.

Because the UK constitution is uncodified, it is often described as flexible. Constitutional norms may be altered by ordinary statute, without the need for special majorities or referendums. Parliament, as the supreme law-making body, may legislate on any subject, including constitutional fundamentals. As Dicey wrote in the late nineteenth century, "Parliament has … the right to make or unmake any law whatever; and further, no person or body is recognised by the law … as having a right to override or set aside the legislation of Parliament." The doctrine of parliamentary sovereignty (examined further in later weeks) remains the central organising principle, albeit subject to contemporary qualification by membership of international legal regimes and devolution settlements.

Yet flexibility is accompanied by a degree of uncertainty. The absence of a canonical text means that identifying what the constitution is often requires synthesis of disparate materials. Conventions—binding as a matter of political obligation, but not enforceable in the courts—regulate many critical relationships, including the formation of governments, the conduct of ministers, and the royal prerogative. Works of authority, such as Erskine May's Parliamentary Practice and the Cabinet Manual, provide guidance but do not possess the formal status of statute or judgment.

This note examines the sources from which the UK constitution is constructed, the historical evolution that gave rise to its uncodified character, and the conceptual debate over whether the constitution is better understood as political or legal in character. Understanding the nature and sources of the constitution is foundational to grasping parliamentary sovereignty, the rule of law, separation of powers, and the modern constitutional settlement, all of which will recur throughout this course.

The uncodified character of the UK constitution reflects centuries of incremental evolution rather than a single founding moment. Unlike polities born of revolution or reconstitution—the United States in 1787, France in 1789, Germany in 1949—the UK has experienced constitutional continuity punctuated by struggle and settlement, but never by wholesale replacement.

The Norman Conquest of 1066 established a strong centralised monarchy. Over subsequent centuries, power oscillated between Crown and Parliament. Magna Carta 1215, though largely of symbolic rather than practical force today, is often cited as the first statutory constraint upon the Crown, establishing that the monarch was not above the law and that taxation required consent. The medieval period saw the gradual emergence of Parliament as an institution: by the late thirteenth century, the Model Parliament of 1295 included representatives of counties and boroughs alongside the nobility and clergy.

The seventeenth century witnessed acute conflict over sovereignty and legitimacy. The constitutional struggles of the Stuart period culminated in civil war, regicide, and the temporary abolition of the monarchy. The Restoration of 1660 and the Glorious Revolution of 1688 were pivotal. The Bill of Rights 1689 and the Claim of Right Act 1689 (Scotland) asserted parliamentary supremacy over the Crown in critical areas: the monarch could not suspend laws, levy taxation, or maintain a standing army in peacetime without parliamentary consent. The Act of Settlement 1701 secured judicial independence, providing that superior judges held office quamdiu se bene gesserint and could be removed only by address of both Houses of Parliament.

In the eighteenth and nineteenth centuries, further incremental change reshaped the balance of power. The Great Reform Act 1832 broadened the franchise and redistributed seats, beginning a process of democratisation continued by the Representation of the People Acts of 1867, 1884, 1918, and 1928, which progressively extended voting rights to working-class men and eventually to women. The Parliament Acts 1911 and 1949 curtailed the veto power of the House of Lords, subordinating it to the elected Commons.

The twentieth and twenty-first centuries brought statute-led constitutional innovation: the European Communities Act 1972 (membership of the EEC, later EU), devolution legislation (Scotland Act 1998, Government of Wales Act 1998, Northern Ireland Act 1998), the Human Rights Act 1998 (incorporation of the European Convention on Human Rights), and the Constitutional Reform Act 2005 (creation of the UK Supreme Court and reform of the office of Lord Chancellor). The EU (Withdrawal) Act 2018 and subsequent Brexit legislation marked a constitutional rupture with the supranational legal order.

This history of evolution, not revolution, explains why the UK has no codified constitution. There has been no single moment demanding a fresh start; instead, constitutional norms have accumulated in layers, each deposited by historical contingency and political compromise.

The uncodified constitution

The defining characteristic of the UK constitution is that it is uncodified. This means there is no single written instrument of superior legal status from which all constitutional rules derive. Instead, the constitution comprises multiple sources, none of which enjoys formal entrenchment.

An uncodified constitution is not synonymous with an unwritten one. Much of the UK constitution is in fact written—statutes such as the Bill of Rights 1689, the Parliament Acts, the Human Rights Act 1998, and the devolution statutes are written law. What is absent is codification: the reduction of constitutional principles to a single authoritative text, hierarchically superior to ordinary legislation.

The flexibility of an uncodified constitution permits adaptation. A simple majority in Parliament may amend or repeal constitutional statutes. Fixed-term Parliaments Act 2011 was repealed by the Dissolution and Calling of Parliament Act 2022 without special procedure. This adaptability is prized by some as enabling responsiveness to changing circumstances. It is criticised by others as lacking the stability and rights-protection afforded by entrenched bills of rights.

The sources of the constitution

The UK constitution draws on five principal sources:

(i) Statute

Acts of Parliament are the primary source of written constitutional law. Statutes regulate the composition and powers of institutions (Parliament Acts 1911 and 1949, House of Lords Act 1999, Constitutional Reform Act 2005), the relationship between the UK and devolved administrations (Scotland Act 1998, etc.), and fundamental rights (Human Rights Act 1998). Because of parliamentary sovereignty, statute takes precedence over common law and prerogative.

There is no formal hierarchy of statutes. The concept of a "constitutional statute" was articulated obiter by Laws LJ in Thoburn v Sunderland City Council [2002] EWHC 195 (Admin), where he suggested that constitutional statutes—those conditioning the legal relationship between citizen and state or enlarging fundamental rights—may not be impliedly repealed. This proposition remains contested and has not been authoritatively endorsed by the Supreme Court.

(ii) Common law

Case law, developed by the courts over centuries, supplies important constitutional principles. The common law has recognised:

Case law plays a constitutive role in UK constitutional law, establishing and elaborating fundamental principles. The following decisions are foundational to understanding the nature and sources of the constitution.

Entick v Carrington (1765)

This case stands as an early and powerful statement of the rule of law and the limits of executive power. Secretary of State Lord Halifax issued a warrant authorising King's messengers to search Entick's premises and seize his papers. Entick sued in trespass. The Crown argued that executive necessity justified the search. Lord Camden CJ held that the warrant was unlawful: neither statute nor common law authorised it, and executive officers possessed no power to act without legal foundation. The case affirmed that state power must be grounded in law and that individuals possess residual liberty unless law provides otherwise.

Attorney General v Jonathan Cape Ltd [1976] QB 752

This case concerned the proposed publication of the diaries of Richard Crossman, a former cabinet minister. The Attorney General sought an injunction to restrain publication on the ground that it would breach the convention of collective cabinet responsibility. Lord Widgery CJ acknowledged that constitutional conventions exist and may inform legal obligations (for example, the law of confidence), but held that conventions themselves are not enforceable in court. The case clarified the boundary between law and convention, a distinction central to the UK's constitutional structure.

R v Secretary of State for the Home Department, ex parte Fire Brigades Union [1995] 2 AC 513

The Home Secretary announced that he would not bring into force a statutory scheme of criminal injuries compensation and would instead operate a less generous prerogative scheme. The House of Lords held, by a majority, that the minister's decision was unlawful. Once Parliament had legislated to create a statutory scheme, the prerogative power in the same field was displaced, and ministers were under a duty not to frustrate Parliament's intention. The decision illustrates the subordination of the prerogative to statute and the reviewability of prerogative decisions.

R (Jackson) v Attorney General [2005] UKHL 56

The Hunting Act 2004, which banned hunting wild mammals with dogs, was passed using the Parliament Act 1949 procedure without the consent of the House of Lords. Claimants challenged its validity, arguing that the 1949 Act itself was invalid because it had been enacted using the 1911 Act's procedure. The House of Lords unanimously rejected the challenge, holding that the 1911 Act had redefined Parliament for certain purposes and that the 1949 Act was validly enacted. Obiter remarks are significant. Lord Steyn suggested that parliamentary sovereignty is a construct of the common law, and that in extreme circumstances—such as an attempt to abolish judicial review or subvert the democratic basis of the constitution—courts might decline to apply an Act of Parliament. Lord Hope spoke of the supremacy of Parliament being a creation of the common law. These dicta have fuelled academic debate over whether parliamentary sovereignty is absolute or subject to fundamental common law limits.

R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5 (Miller I)

The government argued that ministers could trigger Article 50 TEU, initiating the UK's withdrawal from the EU, by prerogative power. The Supreme Court held, by a majority of 8–3, that an Act of Parliament was required. The European Communities Act 1972 had conferred EU law rights on individuals; these rights could not be removed by executive action alone. The prerogative cannot be used to alter domestic law. The decision reaffirmed parliamentary sovereignty and the principle that rights conferred by statute may be withdrawn only by statute. The Court also held that the Sewel Convention, though politically significant, was non-justiciable.

R (Miller) v Prime Minister; Cherry v Advocate General for Scotland [2019] UKSC 41 (Miller II)

In September 2019, the Prime Minister advised the Queen to prorogue Parliament for five weeks during the critical period before the UK's scheduled withdrawal from the EU. The Supreme Court unanimously held the prorogation unlawful. The Court identified two fundamental constitutional principles: parliamentary sovereignty and parliamentary accountability of the executive. Prorogation is a prerogative power, but it is justiciable when its exercise prevents Parliament from performing its functions. The length and timing of this prorogation had the effect of frustrating Parliament's ability to scrutinise the executive. The advice to prorogue was unlawful, and the prorogation was void. The decision represents an assertion of judicial authority to review prerogative acts affecting the core functions of Parliament and is among the most significant constitutional cases in modern times.

AXA General Insurance Ltd v Lord Advocate [2011] UKSC 46

This case concerned a challenge to an Act of the Scottish Parliament abolishing the right to damages for pleural plaques. The Supreme Court held that Acts of the Scottish Parliament, though primary legislation for the purposes of the Human Rights Act, are subordinate legislation from a UK constitutional perspective and are subject to judicial review for compatibility with retained EU law, ECHR rights, and the scope of devolved competence. Obiter dicta addressed whether an Act of the UK Parliament could be reviewed for irrationality or violation of the rule of law. Lord Hope doubted that the UK Parliament could be reviewed on substantive grounds; Lord Reed suggested that an extreme and wholly arbitrary statute might be vulnerable, though such a case is unlikely ever to arise. The case reflects ongoing judicial consideration of the limits, if any, on parliamentary sovereignty.

See practice questions below.

See further reading below.