Introduction
The United Kingdom's constitution is famously uncodified, and at its heart has traditionally lain the principle of parliamentary sovereignty. As articulated by A.V. Dicey, this principle holds that Parliament has the power to make or unmake any law whatsoever, and that no person or body is recognised by the law of England as having a right to override or set aside the legislation of Parliament (Dicey, 1915). A key consequence of this is the doctrine of implied repeal, which states that if two Acts of Parliament conflict, the later Act is presumed to have implicitly repealed the earlier one. However, the landmark case of Thoburn v Sunderland City Council [2003] QB 151 challenged this orthodox view by introducing a hierarchy of statutes, distinguishing between ‘ordinary’ statutes and ‘constitutional’ statutes. This essay will explain the Thoburn doctrine and the concept of constitutional statutes. It will argue that while the doctrine is a significant judicial development that attempts to protect fundamental laws, its constitutional basis is not entirely settled, and it creates a tension with the traditional Diceyan view of parliamentary sovereignty.
The Orthodox Doctrine of Implied Repeal
The traditional understanding of parliamentary sovereignty means that no Parliament can bind its successors. If a Parliament passes an Act, a later Parliament can always amend or repeal it. The doctrine of implied repeal is a practical rule of statutory interpretation that flows from this principle. It ensures that the will of the most recent Parliament is the one that is given effect by the courts. As held in Vauxhall Estates Ltd v Liverpool Corporation [1932] 1 KB 733, where two Acts are inconsistent, "the earlier must be taken to be impliedly repealed by the later". This was confirmed in Ellen Street Estates Ltd v Minister of Health [1934] 1 KB 590, where Maugham LJ stated that the legislature "cannot, according to our constitution, bind itself as to the form of subsequent legislation". For much of the twentieth century, this rule was considered absolute; no Act was seen as having a higher status than any other, and all were equally vulnerable to repeal by a later, inconsistent statute. This provided a clear, if rigid, framework for the courts when faced with statutory conflicts.
The Emergence of the Thoburn Doctrine
The challenge to this orthodoxy came in the case of Thoburn, often referred to as the "Metric Martyrs" case. The case concerned traders who were prosecuted for using imperial measurements (pounds and ounces) instead of metric ones. They argued that the Weights and Measures Act 1985, which permitted the use of imperial measures, had implicitly repealed parts of the European Communities Act 1972 (ECA 1972), which required the UK to implement EU directives mandating metric units. The traders' argument was based on the classic doctrine of implied repeal: the 1985 Act was later than the 1972 Act, so it should prevail.
The Divisional Court rejected this argument. In his judgment, Laws LJ developed a new theory of constitutional statutes. He proposed that the UK’s statutes could be divided into two categories: "ordinary" statutes and "constitutional" statutes. While ordinary statutes could be impliedly repealed as per the traditional rule, constitutional statutes could not. He defined constitutional statutes as those which "(a) condition the legal relationship between citizen and state in some general, overarching manner, or (b) enlarge or diminish the scope of what we would now regard as fundamental constitutional rights" (Thoburn, at [62]). Because of their fundamental nature, Laws LJ argued that such statutes could only be repealed by express language in a subsequent statute, or by an overwhelming inconsistency that makes it clear that Parliament must have intended to repeal the constitutional statute. Simply passing a later Act that conflicts with it is not enough.
Identifying Constitutional Statutes
Laws LJ provided a non-exhaustive list of statutes he considered to be ‘constitutional’. This included historic documents like Magna Carta and the Bill of Rights 1689, as well as modern Acts such as the Acts of Union 1707, the Human Rights Act 1998, the Scotland Act 1998, and, crucially for the case, the European Communities Act 1972. The ECA 1972 was deemed constitutional because it fundamentally altered the legal landscape by incorporating EU law into the UK domestic legal system, thereby changing the relationship between the citizen, the UK government, and a new source of law in Europe.
The criteria for identifying a constitutional statute remain somewhat general, which has led to some academic debate about the doctrine's certainty (Elliott, 2002). However, the central idea is that certain Acts are so fundamental to the structure of the state and the rights of its citizens that the courts should presume Parliament does not intend to repeal them by accident or implication. This requires Parliament to be explicit if it wishes to undo such a significant piece of legislation. This judicial approach has been seen by some as a necessary protection for the rule of law in a country without a written constitution (Allan, 2003).
The Doctrine's Reception and Impact
The Thoburn doctrine, though originating in the Divisional Court, has since been referenced with approval in higher courts, suggesting it has gained significant judicial acceptance. Most notably, in the case of R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5, the Supreme Court explicitly referred to the ECA 1972 as a "constitutional statute" and acknowledged its special status. The court noted that the Act had created a new source of law and had a "fundamental" impact on the UK’s constitutional arrangements, echoing the reasoning of Laws LJ.
Furthermore, in H v Lord Advocate [2012] UKSC 24, the Supreme Court considered the status of the Scotland Act 1998. While not deciding the point directly, Lord Hope suggested that it would be open to the UK Parliament to legislate in a way that would prevent the Scotland Act from being impliedly repealed, lending further support to the idea that certain statutes can be given a higher status. These cases indicate that the judiciary has become more willing to recognise a hierarchy of statutes and to qualify the traditional doctrine of implied repeal in order to protect what it sees as key constitutional legislation. This marks a shift from a purely formal view of sovereignty to one that also considers the substantive importance of certain laws.
An Unsettled Constitutional Position
Despite its growing acceptance, the Thoburn doctrine raises important constitutional questions. The most significant is its apparent conflict with the Diceyan concept of parliamentary sovereignty. By creating a class of statutes that are immune from implied repeal, the courts have effectively imposed a "manner and form" requirement on Parliament: it can still repeal these Acts, but it must do so expressly. Some scholars argue that this is a direct challenge to the idea that Parliament cannot be bound, representing a significant transfer of power from the legislature to the judiciary, as it is judges who decide which statutes are "constitutional" (Wade, 2003).
On the other hand, it can be argued that the doctrine does not destroy parliamentary sovereignty, but merely refines it. Parliament remains the ultimate sovereign authority because it can expressly repeal any constitutional statute it chooses. The Thoburn doctrine simply ensures that Parliament does so intentionally and with full awareness of the consequences. It acts as a judicial interpretive presumption that Parliament is "not to be taken to have legislated in a way that interferes with fundamental rights or the constitutional structure without making its intention to do so crystal clear" (Elliott, 2004, p. 352). From this perspective, the doctrine supports, rather than subverts, the democratic process by promoting legislative clarity on matters of great constitutional importance. Nevertheless, the vague criteria for what constitutes a constitutional statute and the judicial power to make this determination remain points of contention and create a degree of legal uncertainty.
Conclusion
The Thoburn doctrine of constitutional statutes represents a significant evolution in UK constitutional law. It moves away from the rigid, traditional view of implied repeal by establishing a hierarchy of Acts of Parliament, where fundamental statutes are protected from accidental or casual repeal. By requiring express language to repeal a constitutional statute, the courts have created a procedural safeguard for laws that are seen as foundational to the UK's legal and political order. While the doctrine has been endorsed in subsequent high-profile cases like Miller, its relationship with the orthodox principle of parliamentary sovereignty remains complex. It can be viewed either as a judicial challenge to Parliament's absolute power or as a common-sense interpretive rule that enhances legislative responsibility. Ultimately, the doctrine shows the adaptability of the UK's unwritten constitution, demonstrating the judiciary’s role in developing principles that seek to protect the rule of law and fundamental rights in a modern state.
References
Allan, T. R. S. (2003) Constitutional Justice: A Liberal Theory of the Rule of Law. Oxford: Oxford University Press.
Dicey, A. V. (1915) Introduction to the Study of the Law of the Constitution. 8th edn. London: Macmillan.
Elliott, M. (2002) 'The Demise of Parliamentary Sovereignty? The Implications of the Human Rights Act 1998'. In: Jowell, J. and Cooper, J. (eds.) Understanding Human Rights Principles. Oxford: Hart Publishing.
Elliott, M. (2004) 'United Kingdom: Parliamentary Sovereignty Under Pressure'. International Journal of Constitutional Law, 2(2), pp. 545-627.
Ellen Street Estates Ltd v Minister of Health [1934] 1 KB 590.
H v Lord Advocate [2012] UKSC 24.
R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5.
Thoburn v Sunderland City Council [2003] QB 151.
Vauxhall Estates Ltd v Liverpool Corporation [1932] 1 KB 733.
Wade, H. W. R. (2003) 'Sovereignty: Revolution or Evolution?'. Law Quarterly Review, 119, pp. 568-574.
