Introduction
The structure of government in the United Kingdom is a complex arrangement of institutions and relationships that has evolved over centuries. Understanding this structure requires an analysis of both the ‘arms’ of government – the legislature, executive, and judiciary – and the ‘tiers’ of government, which refers to the vertical distribution of power between central, devolved, and local authorities. This essay will discuss these components of the UK state, examining their functions, the ways they are similar and different, and their relative hierarchy. The central argument is that while the UK constitution does not adhere to a strict doctrine of separation of powers, particularly regarding the executive and legislature, it relies on a system of ‘checks and balances’ to distribute power and prevent its concentration. This discussion will demonstrate that a full understanding of these arms and tiers is essential to explain how the core principles of constitutionalism operate in practice within the UK.
The Arms of Government and the Separation of Powers
The principle of the separation of powers, most famously articulated by Montesquieu, suggests that state power should be divided between three distinct branches or ‘arms’ to protect liberty (Montesquieu, 1748). These are the legislature, which makes the law; the executive, which puts the law into effect and runs the country; and the judiciary, which interprets and applies the law. In the UK, these functions are carried out by Parliament, His Majesty's Government, and the courts, respectively. The ideal form of this doctrine requires that the same persons should not form part of more than one of the three arms, that one arm should not control or interfere with the work of another, and that the functions of each arm should be distinct.
However, the UK constitution is more accurately described as exhibiting a ‘fusion of powers’ rather than a strict separation (Bagehot, 1867). This is most apparent in the relationship between the executive and the legislature. The Prime Minister and the majority of government ministers are members of, and are drawn from, the legislature (either the House of Commons or the House of Lords). This overlap in personnel means that the executive, far from being separate, is deeply embedded within Parliament. This fusion is a core feature of the Westminster model of government, where the government is accountable to Parliament but also, in practice, often commands it, especially when it has a large majority. This has led to descriptions of the UK system as an ‘elective dictatorship’ (Hailsham, 1976), where the executive can dominate the legislative process.
By contrast, the separation between the judiciary and the other two arms of government is more pronounced. The principle of judicial independence is a cornerstone of the UK constitution, ensuring that judges are free from political pressure when deciding cases. The Constitutional Reform Act 2005 (CRA 2005) significantly strengthened this separation. It reformed the office of the Lord Chancellor, who was previously a senior judge, a member of the cabinet (executive), and the speaker of the House of Lords (legislature). The Act also created the UK Supreme Court, separating the country’s highest court of appeal from the House of Lords, thereby providing a clear institutional and physical separation between the senior judiciary and Parliament.
A System of Checks and Balances
Given the fusion of the executive and legislative branches, the UK constitution relies heavily on a system of checks and balances to control power. This system ensures that, despite the overlaps, each branch has some power to limit the actions of the others, creating a state of interdependence.
Parliament’s primary check on the executive is the principle of political accountability. Ministers are accountable to Parliament for their decisions and the performance of their departments, through mechanisms such as Prime Minister’s Questions, parliamentary debates, and the work of departmental select committees. These committees scrutinise the policies and expenditure of government departments and can produce critical reports that influence public and political debate (Le Sueur, Sunkin and Murkens, 2022). Ultimately, the House of Commons holds the power to remove a government through a vote of no confidence, although this is a rare event in practice.
The judiciary provides a crucial legal check on the executive through the mechanism of judicial review. This allows judges to review the lawfulness of actions taken by public bodies, including government ministers. If a court finds that a decision was made illegally, irrationally, or with procedural impropriety, it can declare the action unlawful and quash the decision ( Council of Civil Service Unions v Minister for the Civil Service [1985] AC 374). The Human Rights Act 1998 further empowered the judiciary, allowing it to scrutinise primary legislation for its compatibility with the European Convention on Human Rights. While courts cannot strike down an Act of Parliament due to the doctrine of parliamentary sovereignty, they can issue a ‘declaration of incompatibility’ under section 4 of the Act, placing political pressure on Parliament to amend the legislation. This creates a dialogue between the judiciary and the legislature, demonstrating a check on legislative power that falls short of the powers held by courts in countries with codified constitutions.
There are also checks in the other direction. For instance, the executive has some control over the legislative timetable in Parliament, and the judiciary's power is limited by the fact that judges can only interpret and apply the law made by Parliament; they cannot create it from scratch.
The Tiers of Government: Devolution and Vertical Checks
Beyond the horizontal separation of powers, the UK also has a vertical distribution of power across different ‘tiers’ of government. This refers to the relationship between the central UK government in Westminster and the devolved administrations in Scotland, Wales, and Northern Ireland, as well as local government across the country.
Devolution, introduced in the late 1990s, transferred significant legislative and executive powers from the UK Parliament to the Scottish Parliament, the Senedd Cymru (Welsh Parliament), and the Northern Ireland Assembly. These devolved bodies have power over domestic policy areas such as health, education, and local government. This has created a quasi-federal structure, where power is shared between different levels of government. Devolution acts as a check on the power of the central government by creating alternative sites of democratic legitimacy and policy-making.
However, the UK is not a federal state. The UK Parliament remains legally sovereign, meaning it retains the theoretical power to legislate for the devolved nations, even on devolved matters, and could, in principle, abolish the devolved institutions. The relationship is governed by conventions, most notably the Sewel Convention, which states that the UK Parliament will "not normally" legislate on a devolved matter without the consent of the devolved legislature. The Supreme Court confirmed in the Miller case that this convention is a political rule and is not legally enforceable by the courts (R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5). This confirms a clear hierarchy: the devolved tiers are subordinate to the central UK Parliament, even if in practice they operate with a high degree of autonomy. Local government represents a further tier, but its powers are granted entirely by Parliament and it is subject to significant control from central government, limiting its role as an effective check on central power.
Conclusion
In conclusion, understanding the arms and tiers of the UK government is fundamental to explaining the practical application of its guiding constitutional principles. The system is not one of strict separation but of a complex interplay and fusion, particularly between the executive and legislature. This structural reality means that the control of power depends not on institutional separation, but on a web of checks and balances. These checks operate horizontally between the legislature, executive, and judiciary, with judicial review and parliamentary scrutiny being key mechanisms. They also operate vertically, with the devolved tiers of government providing a significant, albeit politically rather than legally entrenched, counterweight to the centralisation of power in Westminster. The UK’s constitutional arrangements, therefore, favour flexibility and political accountability over the rigid legalism of a codified constitution with a strict separation of powers. The differences, functions, and hierarchies of the arms and tiers of government all combine to create a distinctive system of governance where power is distributed and checked, even where it is not strictly separated.
References
Bagehot, W. (1867) The English Constitution. London: Chapman and Hall.
Barnett, H. (2017) Constitutional & Administrative Law. 12th edn. London: Routledge.
Council of Civil Service Unions v Minister for the Civil Service [1985] AC 374.
Hailsham, Lord. (1976) ‘Elective Dictatorship’. The Listener, 21 October.
Le Sueur, A., Sunkin, M. and Murkens, J. (2022) Public Law: Text, Cases, and Materials. 5th edn. Oxford: Oxford University Press.
Montesquieu, C. (1748) The Spirit of the Laws.
R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5.
Statutes
Constitutional Reform Act 2005.
Human Rights Act 1998.
