Sources and nature of the constitution

Constitutional Law begins with an apparently simple question: where is the constitution? In many legal systems the answer is literal. The constitution is a single enacted text, superior to ordinary legislation, judicially enforceable against the legislature, executive and courts. The United Kingdom is different. Its constitution is not contained in one document. It is an accumulation of statutes, common law principles, parliamentary practices, prerogative powers, conventions, political understandings, judicial decisions, and institutional habits. This does not make it unreal. It makes it more difficult to identify, describe and evaluate.

For Cambridge Part IA purposes, the immediate task is not to memorise a list of constitutional materials, but to understand how those materials operate as sources of legal and political authority. Constitutional Law is concerned with the relationship between citizen, Parliament, executive and courts. It asks: who may exercise public power; from what source; subject to what limits; and by what institutional mechanism those limits may be enforced. The same questions reappear throughout the paper: judicial review, human rights, parliamentary sovereignty, prerogative powers, devolution, separation of powers and the rule of law are all applications of the foundational inquiry begun here.

The United Kingdom constitution is often called uncodified rather than unwritten. That is more accurate. Much of it is written: the Bill of Rights 1688, Acts of Union, Parliament Acts, European Communities Act 1972, Human Rights Act 1998, Constitutional Reform Act 2005, devolution statutes, Fixed-term Parliaments Act 2011 and its repeal, and the European Union (Withdrawal) Act 2018 are all written instruments. What the constitution lacks is comprehensive codification and entrenched legal supremacy in a single constitutional instrument. Ordinary Acts of Parliament can alter constitutional arrangements unless special political or legal constraints apply. That feature makes parliamentary sovereignty central, though its meaning and limits are contested.

A useful first distinction is between legal rules and constitutional conventions. Legal rules are enforceable by courts. Conventions are non-legal rules governing constitutional behaviour: for example, that the monarch acts on ministerial advice, that ministers are accountable to Parliament, and that the House of Lords normally respects manifesto legislation under the Salisbury convention. Conventions may be recognised by courts as part of the constitutional background, but courts do not enforce them as law. This distinction is indispensable, but not absolute in practical significance: a convention may be politically more powerful than a legal rule.

A second distinction is between sources and principles. Sources tell us where constitutional norms are found. Principles tell us how those norms should be understood. Parliamentary sovereignty, the rule of law, responsible government, separation of powers, representative democracy, legality, constitutional accountability and protection of rights are principles which structure legal reasoning even where no single written text announces them. The modern constitution is therefore neither purely political nor purely legal. It is a working settlement in which legal doctrine, institutional restraint, democratic legitimacy and judicial supervision interact.

The historical development of the constitution explains why the United Kingdom has a dispersed constitutional order. It was not designed at one moment. It emerged from conflict over the location and limitation of public power. The medieval and early modern struggles between Crown, Parliament and courts generated several enduring ideas: government must have lawful authority; taxation and legislation require parliamentary consent; judges may determine whether executive action is legally justified; and political power is legitimate only when exercised through recognised institutions.

Magna Carta 1215 is often over-romanticised, but it remains symbolically important. Its modern legal content is limited, yet it stands for the idea that public power may be constrained by law. The seventeenth century is more directly important. The Petition of Right 1628 challenged forced loans, arbitrary imprisonment and martial law. The Civil War, Commonwealth, Restoration and Glorious Revolution transformed the balance between Crown and Parliament. The Bill of Rights 1688 and Claim of Right 1689 settled central principles: the Crown could not suspend or dispense with laws without parliamentary authority; taxation required grant of Parliament; and parliamentary proceedings were protected from judicial interference.

The eighteenth and nineteenth centuries consolidated parliamentary government. Cabinet government developed from political practice rather than statutory design. The monarch’s personal discretion receded; ministers became responsible to Parliament; and the House of Commons became the dominant political chamber. The franchise expanded through reform legislation, and democracy entered a constitutional structure originally built around monarchy, aristocracy and parliamentary privilege. This is characteristic of the British constitution: old legal forms persisted while political substance changed.

A.V. Dicey’s late nineteenth-century account remains unavoidable. Dicey identified parliamentary sovereignty and the rule of law as the two leading features of the constitution. His account was powerful because it made the constitution intelligible in juristic terms: Parliament may make or unmake any law; no person or body may override legislation; all persons, including officials, are subject to ordinary law administered by ordinary courts. Yet Dicey’s account was also partial. It underplayed conventions, responsible government, party discipline, the administrative state, imperial dimensions, and later the welfare state. It is a starting point, not a conclusion.

The twentieth century complicated the old model. The growth of the executive made formal parliamentary control less convincing. Delegated legislation, administrative discretion and national security decision-making expanded government power. Judicial review developed to control legality, procedural fairness and rationality. The European Communities Act 1972 introduced a statutory channel through which EU law prevailed over inconsistent domestic law so long as the Act remained in force. The Human Rights Act 1998 altered rights adjudication by requiring courts, so far as possible, to interpret legislation compatibly with Convention rights and by permitting declarations of incompatibility. Devolution statutes created legislatures and executives in Scotland, Wales and Northern Ireland subject to statutory limits. The Constitutional Reform Act 2005 altered the office of Lord Chancellor, created the Supreme Court and gave statutory recognition to the rule of law.

Recent constitutional history has intensified foundational questions. Brexit required courts to address whether ministers could use prerogative powers to alter domestic law and whether prorogation could be judicially reviewed. The Supreme Court’s decisions in Miller and Miller/Cherry are not merely Brexit cases; they concern the legal architecture of the constitution. They show a court willing to articulate constitutional principles while insisting that it is applying law, not politics. That is the modern setting for this topic.

The first principle is parliamentary sovereignty. In its orthodox Diceyan form, Parliament has the legal right to make or unmake any law, and no person or body has legal authority to override or set aside an Act of Parliament. This proposition has three elements: unlimited legislative competence, no binding of successors, and judicial obedience to valid Acts. It is not a claim that Parliament is politically omnipotent. Elections, party discipline, international commitments, devolution, rights culture, markets, administrative capacity and political legitimacy all constrain Parliament in practice. The doctrine concerns legal authority.

The orthodox view is challenged at the margins. Constitutional statutes, EU membership before withdrawal, devolution, human rights adjudication and judicial statements in Jackson have all raised questions about whether sovereignty is absolute, self-embracing, continuing, common law-based, or politically constructed. For Part IA, the safest formulation is this: the courts continue to treat Acts of the King-in-Parliament as the highest source of domestic law, but the manner in which constitutional statutes are interpreted and repealed demonstrates a more sophisticated hierarchy of constitutional significance within the statute book.

The second principle is the rule of law. At its narrowest, it requires that government act according to law and that legal powers be authorised and limited. Entick v Carrington remains the classic illustration: state officials could not justify entry and seizure without lawful authority. In a formal conception, the rule of law demands legality, clarity, prospectivity, stability, access to courts and equality before ordinary law. In a thicker conception, it also requires protection of fundamental rights, fairness, participation and limits on arbitrary power. The United Kingdom constitution contains both tendencies. Courts often rely on legality, access to justice and fair procedures, while remaining cautious about turning the rule of law into an open-ended licence to invalidate legislation.

The cases on this topic should be learned not as isolated propositions but as a sequence of constitutional problems. Entick v Carrington establishes the negative premise of executive power: officials must point to lawful authority for coercive action. It is a rule of legality and a protection against arbitrary administration. The case is frequently invoked because it captures the common law’s hostility to unlicensed state intrusion.

Attorney General v De Keyser’s Royal Hotel concerns the relationship between statute and prerogative. Where Parliament has legislated in an area previously governed by prerogative power, ministers cannot use the prerogative to escape the statutory scheme. This is an ordering rule among sources: statute is superior to prerogative. The importance of the case extends beyond wartime requisition. It underlies modern analysis of executive power and was central to the reasoning in Miller.

CCSU v Minister for the Civil Service marks the modern judicial review position on prerogative powers. The old idea that prerogative powers were immune because of their source was rejected. Reviewability depends primarily on subject matter. Some prerogative powers, such as national security or treaty-making, may remain non-justiciable in particular respects, but the mere fact that the legal source is prerogative does not preclude review.

Factortame is indispensable for understanding the relationship between parliamentary sovereignty and EU membership. The House of Lords disapplied inconsistent provisions of an Act of Parliament because the European Communities Act 1972 required domestic courts to give effect to directly effective EU law. On one view, this qualified sovereignty. On the orthodox statutory view, it represented Parliament’s own instruction, reversible by later repeal. The latter view became influential in Thoburn and in post-Brexit reasoning.

Thoburn introduced the category of constitutional statutes. Laws LJ distinguished ordinary statutes from statutes conditioning the legal relationship between citizen and state or enlarging or diminishing fundamental rights. Such statutes are not immune from repeal, but they are not subject to implied repeal. Express words, or words so specific that repeal is irresistible, are required. This doctrine is central to the modern uncodified constitution because it creates hierarchy of interpretive treatment without abandoning parliamentary sovereignty.

Jackson is important because several Law Lords questioned the absolute nature of sovereignty. The validity of the Hunting Act 2004 was upheld, but dicta suggested that parliamentary sovereignty might be a common law construct and that extreme legislation might raise deeper constitutional questions. The case should be handled carefully. It did not authorise courts to strike down Acts of Parliament. Its significance lies in the judicial willingness to debate ultimate constitutional fundamentals.

Miller and Miller/Cherry show the Supreme Court articulating constitutional principles in contemporary institutional conflict. Miller held that ministers could not use prerogative powers to give notice under Article 50 where doing so would alter domestic law and statutory rights. Miller/Cherry held prorogation justiciable and unlawful where it frustrated Parliament’s constitutional functions without reasonable justification. Both decisions demonstrate that an uncodified constitution may still generate legal limits on executive action.

See practice questions section below.

See further reading section below.