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Because the UK has no single codified document, its constitution must be assembled from a number of distinct sources. The Edexcel specification identifies the principal sources as statute law, common law, conventions, works of authority, and historically EU law and treaties. Understanding these sources is essential, because the constitution's authority is dispersed across statutes, judicial decisions, customary practice, scholarly texts and (until Brexit) European Union law. Each source carries a different kind of weight — legal or merely political — and the tensions between them generate many of the debates examined in Section A of Paper 2. A strong candidate can not only name the sources but explain their relative authority, illustrate each with precise examples, and evaluate the consequences of relying on such a varied and unentrenched body of rules.
Statute law is the most important source of the UK constitution. Statutes are laws passed by Parliament — that is, approved by the House of Commons and the House of Lords and granted Royal Assent — and they are the highest form of law in the UK legal system. Because Parliament is sovereign, any constitutional rule contained in a statute takes precedence over every other source. Where statute and common law conflict, statute prevails; where statute and convention conflict, the statute is what the courts will enforce.
Key constitutional statutes include:
| Statute | Year | Significance |
|---|---|---|
| Magna Carta | 1215 | Limited the monarch's power; early due-process guarantees |
| Bill of Rights | 1689 | Established parliamentary supremacy over the Crown; free elections |
| Act of Settlement | 1701 | Protestant succession; strengthened judicial independence |
| Acts of Union | 1707 | United England and Scotland under one Parliament |
| Parliament Acts | 1911, 1949 | Reduced the Lords' veto to a delaying power |
| European Communities Act | 1972 | Incorporated EEC/EU law (repealed on Brexit) |
| Scotland Act / Government of Wales Act / Northern Ireland Act | 1998 | Created the devolved legislatures |
| Human Rights Act | 1998 | Incorporated the ECHR into UK law |
| House of Lords Act | 1999 | Removed most hereditary peers (92 retained) |
| Constitutional Reform Act | 2005 | Created the Supreme Court; reformed the Lord Chancellor |
| Fixed-term Parliaments Act | 2011 | Set five-year fixed terms (repealed 2022) |
Not all statutes are constitutional. The great bulk of legislation deals with ordinary matters of policy — taxation, transport, education and so on. What makes a statute constitutional is that it concerns the structure of government, the relationship between institutions, or the rights of citizens. Some scholars and judges have even suggested that certain "constitutional statutes" (such as the Human Rights Act or the devolution Acts) enjoy a special status and cannot be impliedly repealed by a later, inconsistent Act, but must be expressly repealed. This idea, floated in the Thoburn case (2002), qualifies the strict Diceyan picture without overturning it: it does not entrench these statutes, but it does treat them as more fundamental than ordinary legislation.
A related debate surrounds the Acts of Union 1707, which united England and Scotland. Some commentators argue that the Union created a new Parliament of Great Britain bound by the terms of the Union and that certain provisions are therefore unalterable, which would be an exception to parliamentary sovereignty. The orthodox view, however, is that the Westminster Parliament inherited full sovereignty and may legislate as it wishes. This long-running argument is a useful illustration of how even the foundational statutes of the constitution can be read in competing ways, precisely because there is no codified text to settle the question.
Why statute law is the most important source:
Limitations:
The dominance of statute is itself a consequence of parliamentary sovereignty: because Parliament can make or unmake any law and no body can override it, whatever Parliament enacts becomes the highest constitutional authority. This is why so much of the modern constitution has been built through legislation. The reform programme since 1997 — devolution, the Human Rights Act, the Constitutional Reform Act, House of Lords reform — was delivered almost entirely by statute, steadily increasing the proportion of the constitution that is written down in Acts of Parliament. Some observers describe this as "codification by instalment", though it falls well short of producing a single, entrenched, higher-law document. The key point for evaluation is that statute provides clarity and democratic legitimacy, but offers no special protection: a constitutional statute can be repealed exactly like any ordinary law, as the swift repeal of the Fixed-term Parliaments Act in 2022 demonstrated.
Common law is judge-made law developed through court decisions over many centuries. It rests on legal precedent — the principle (stare decisis) that courts should follow the decisions of higher courts in earlier, similar cases. Common law fills the gaps left by statute and, historically, has been a major source of both governmental power and individual liberty.
Key elements of common law within the constitution:
Royal prerogative powers. These are the historic powers of the Crown, now in practice exercised by or on the advice of ministers, that derive from common law rather than statute. They include the power to make and ratify treaties, to deploy the armed forces and declare war, to grant honours, to issue and withdraw passports, and to appoint ministers. The prerogative is significant because it allows the Executive to act without fresh statutory authority — which is precisely why the courts have progressively brought it under control. In the GCHQ case (Council of Civil Service Unions v Minister for the Civil Service, 1985), the House of Lords confirmed that the exercise of prerogative powers is, in principle, subject to judicial review.
The rule of law. Dicey identified the rule of law as a fundamental constitutional principle, and much of its content is found in common-law doctrine. It holds that everyone, including the government, is subject to the ordinary law; that no one may be punished except for a clear breach of law established before the courts; and that the liberties of individuals are protected through concrete judicial decisions rather than abstract declarations.
Residual rights and liberties. Before the Human Rights Act 1998, many civil liberties — freedom of expression, freedom of assembly, freedom of the person — were protected by common law as residual freedoms: citizens were free to do anything that the law did not specifically prohibit. The courts also developed principles, such as the presumption that statutes do not intend to abolish fundamental rights unless they do so in clear words.
Strengths of common law:
Weaknesses:
The growth of common-law control over the prerogative is one of the most important constitutional developments of recent decades and a rich source of exam examples. The royal prerogative is the most politically sensitive aspect of common law because it allows the Executive to act without going to Parliament. Once regarded as largely beyond the reach of the courts, the prerogative is now firmly subject to judicial scrutiny. In the GCHQ case (1985) the courts established that its exercise can in principle be reviewed. In R (Miller) v Secretary of State for Exiting the EU [2017] the Supreme Court held that the prerogative could not be used to trigger Article 50, because doing so would remove statutory rights — only Parliament could authorise that step. In R (Miller) v The Prime Minister [2019] the Court went further, ruling that the prerogative power to prorogue Parliament is justiciable and was unlawfully exercised when used to frustrate Parliament's functions. Taken together, these decisions show common law actively reshaping the balance between the Executive, Parliament and the courts — a vivid demonstration that judge-made law remains a living source of the constitution.
A further point of evaluation concerns the protection of rights. For centuries the chief guardian of individual liberty in Britain was the common law, through the doctrine of residual freedom and presumptions against the abolition of fundamental rights. This approach had real strengths — it was woven into ordinary law and did not depend on the goodwill of the state — but it also had a fundamental weakness: common-law rights could always be cut back by clear statute, and they offered no positive code of entitlements. The Human Rights Act 1998 therefore marked a shift in how rights are sourced, moving from largely common-law protection towards a statutory framework based on the European Convention. The two now operate together, with common-law rights surviving alongside the Convention rights given effect by the HRA. This interplay between common law and statute in the field of rights is a sophisticated example for essays on the sources of the constitution.
Conventions are unwritten rules of constitutional practice that are regarded as binding but are not legally enforceable. They have grown up over time through repeated practice and shared understandings, and they guide how the institutions of government and the people within them behave. Conventions are arguably the most distinctive feature of an uncodified constitution, because they show how much of the system runs on accepted practice rather than hard law.
What distinguishes a convention from a mere habit is the sense of obligation attached to it: those involved feel bound to follow it and would regard a breach as constitutionally improper, even though no court could enforce compliance. What distinguishes a convention from a law is the absence of legal sanction: conventions are upheld by political pressure, the force of precedent and the fear of constitutional crisis rather than by judicial enforcement. This makes conventions powerful in normal times yet fragile when a determined government chooses to test them.
Key constitutional conventions:
| Convention | Description |
|---|---|
| Collective Cabinet responsibility | All Cabinet ministers must publicly support government policy or resign |
| Individual ministerial responsibility | Ministers are accountable to Parliament for the conduct of their departments |
| The Salisbury Convention | The Lords does not vote down legislation promised in the governing party's manifesto |
| The Sewel Convention | Westminster does not normally legislate on devolved matters without the devolved legislature's consent |
| Royal Assent | The monarch always grants Royal Assent to bills passed by both Houses |
| Appointment of the PM | The monarch appoints as PM the person able to command the confidence of the Commons |
Two of these conventions deserve closer study because they underpin the accountability of the Executive. Collective Cabinet responsibility requires ministers to support government policy in public, or else resign, and it keeps the secrecy of Cabinet discussions so that the government can present a united front; resignations such as those of senior ministers over Brexit policy illustrate the convention in action. Individual ministerial responsibility makes each minister answerable to Parliament for the conduct of their department, traditionally requiring resignation for serious personal or departmental failure. Both conventions are unwritten and unenforceable in law, yet they are central to how Parliament holds government to account — which is exactly why their weakening over time is constitutionally significant.
Why conventions matter:
Limitations of conventions:
Case Study: The Sewel Convention and Brexit. During the Brexit process the UK government legislated on matters affecting devolved competences without the legislative consent of the Scottish Parliament or Senedd. In R (Miller) v Secretary of State for Exiting the EU [2017] the Supreme Court held that, although the Sewel Convention had been recognised in statute by the Scotland Act 2016, it remained a political convention that the courts would not enforce. The ruling vividly demonstrated the vulnerability of conventions in an uncodified system: a recognised, important rule of practice can be set aside without legal consequence.
Should conventions be codified? Because conventions are unwritten and unenforceable, there is a recurring debate about whether they should be written down or even turned into law. Supporters of codifying conventions argue that this would remove ambiguity — for instance, settling exactly when collective responsibility applies or what the Sewel Convention requires — and make breaches easier to identify and resist. Opponents reply that the great virtue of conventions is precisely their flexibility: they can adapt quietly to changing circumstances, whereas writing them into rigid rules might freeze practice and remove the discretion that allows the system to evolve. The partial recognition of the Sewel Convention in statute, and its subsequent treatment by the courts as still merely political, illustrates the difficulty of half-codifying a convention without giving it real legal force.
Because the constitution is uncodified, certain respected scholarly and procedural texts are treated as authoritative guides to constitutional principle and practice. They have no legal force in themselves, but they are widely cited by politicians, officials and even the courts when the meaning of a constitutional rule is in doubt.
Key works of authority:
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