Introduction
The doctrine of the separation of powers is a fundamental principle of constitutional law, advocating for the distribution of state power among distinct institutions to prevent its concentration and abuse. The French jurist Montesquieu is often credited with the classic formulation of this doctrine, proposing a strict division between the legislative, executive, and judicial branches of government. As the quotation from Yuravitch suggests, this pure model is rarely found in practice, and the United Kingdom’s constitution is often cited as a prime example of a system that diverges from it. This essay will discuss Yuravitch's view by first describing the separation of powers and its purpose. It will then examine the relationships between the three branches of the UK state, analysing the extent of separation, overlap, and the system of checks and balances. The essay will argue that while the UK does not adhere to a strict separation of powers, particularly regarding the executive and legislature, it upholds the doctrine's spirit through a complex web of checks and balances that has been strengthened in recent years, especially concerning the judiciary.
The Separation of Powers Doctrine and Its Purpose
The separation of powers doctrine proposes that the functions of the state should be divided between three distinct branches. These are the legislature, which has the function of making law; the executive, which implements and administers the law; and the judiciary, which interprets and applies the law in resolving disputes (Bradley, Ewing and Knight, 2018). The primary purpose of this division is to protect the liberty of the individual by preventing any single body from accumulating excessive power. As Montesquieu famously argued in The Spirit of the Laws, “When the legislative and executive powers are united in the same person, or in the same body of magistrates, there can be no liberty” (Montesquieu, 1748). The doctrine, therefore, aims to create a system of constitutional government where state power is limited and subject to the rule of law. While Montesquieu is the most famous proponent, earlier thinkers like John Locke also identified the need to separate powers, albeit with a less rigid distinction. In the modern context, the doctrine is seen not just as a safeguard against tyranny but also as a means of ensuring governmental efficiency and accountability, with each branch having its own expertise and function.
The Legislature and the Executive
The relationship between the legislature (Parliament) and the executive (the Government) in the UK is the clearest departure from Montesquieu’s model. Instead of a strict separation, the UK constitution is characterised by what Walter Bagehot called a “fusion” of powers (Bagehot, 1867). The most significant overlap is in personnel: the Prime Minister and the vast majority of government ministers are also Members of Parliament (MPs) and sit in the House of Commons. By convention, ministers must be members of either the Commons or the House of Lords. This fusion means that the executive is drawn directly from within the legislature and is not a separate body as it is in the US presidential system.
This overlap gives the executive considerable influence over the legislative process. A government with a stable majority in the House of Commons can be almost certain of passing its legislative programme. The government controls the parliamentary timetable and uses the party whipping system to ensure its MPs vote along party lines. This dominance has led some commentators to describe the UK system as an ‘elective dictatorship’ (Hailsham, 1976), where Parliament’s role is simply to legitimise the executive’s decisions.
However, this fusion is balanced by a series of important checks. The executive is accountable to Parliament. Ministers must answer questions in Parliament, both orally (e.g., Prime Minister's Questions) and in writing. A more effective form of scrutiny is conducted by departmental select committees, which scrutinise the policies and expenditure of government departments and can produce critical reports. The House of Lords, as the second chamber, can also act as a check by delaying and proposing amendments to legislation, forcing the government to reconsider its proposals. Ultimately, the executive only governs with the consent of the House of Commons, and though it is rare, a government can be removed from office by a vote of no confidence. Therefore, while there is a clear fusion of personnel and power, the executive is formally subordinate to and held to account by the legislature.
The Legislature and the Judiciary
The relationship between the legislature and the judiciary has traditionally been more separate than that between the executive and legislature, but historically, there were significant overlaps. The most prominent example was the office of the Lord Chancellor, who was a member of all three branches, and the role of the Law Lords, who were senior judges sitting in the House of Lords, the UK’s highest court and also part of the legislature.
The Constitutional Reform Act 2005 (CRA 2005) fundamentally altered this relationship and moved the UK closer to a formal separation. The Act created a new, separate Supreme Court of the United Kingdom, removing the country's senior judges from Parliament. It also reformed the role of the Lord Chancellor. Furthermore, long-standing rules protect judicial independence from legislative interference. Judges cannot be MPs (House of Commons Disqualification Act 1975) and MPs are forbidden by the sub judice rule from discussing current legal proceedings in Parliament to avoid prejudicing the outcome.
Despite this increased separation, checks and balances remain. The core principle of parliamentary sovereignty means that Parliament is the supreme law-making body and can pass legislation to override common law decisions made by judges. A classic example is the War Damage Act 1965, which was passed to retrospectively overturn the House of Lords' decision in Burmah Oil Co Ltd v Lord Advocate [1965] AC 75. A more modern check exercisable by the judiciary over the legislature is found in the Human Rights Act 1998 (HRA 1998). Under section 3 of the HRA, courts must interpret legislation in a way that is compatible with the European Convention on Human Rights. If this is not possible, senior courts can issue a 'declaration of incompatibility' under section 4. This does not invalidate the Act of Parliament but puts political pressure on Parliament to amend the law. This respects parliamentary sovereignty while allowing the judiciary to check legislation against human rights standards.
The Executive and the Judiciary
The separation between the executive and the judiciary is crucial for upholding the rule of law, as it ensures that the government can be held accountable under the law. As with the legislative-judicial relationship, the CRA 2005 was a landmark piece of legislation in enhancing this separation. Before the Act, the Lord Chancellor, a senior government minister, was head of the judiciary and presided over the judicial appointments system. The CRA 2005 established the independent Judicial Appointments Commission (JAC) to select candidates for judicial office based on merit, removing much of the political patronage that was previously possible. The Act also created a statutory duty on the Lord Chancellor and other ministers to uphold the independence of the judiciary.
The primary check that the judiciary exercises over the executive is the power of judicial review. Through judicial review, the courts can ensure that executive bodies, including government ministers, act lawfully, rationally, and fairly within the powers granted to them by Parliament. Landmark cases like Council of Civil Service Unions v Minister for the Civil Service [1985] 3 All ER 935 established the grounds for review, and courts have shown they are willing to challenge the executive, even on matters of high policy. For example, in R (Miller) v The Prime Minister [2019] UKSC 41, the Supreme Court held that the Prime Minister's advice to the Queen to prorogue Parliament was unlawful. This demonstrates a robust judicial check on executive power.
However, the executive retains some influence. The government initiates legislation that can limit or remove the scope of judicial review (sometimes known as ouster clauses), and the Lord Chancellor (now also the Secretary of State for Justice) still has a role in judicial appointments, albeit a much-reduced one. Furthermore, the executive is responsible for resourcing the justice system, which can have an indirect impact on judicial functions. Nevertheless, the separation is strong and is considered a cornerstone of the UK constitution.
Conclusion
In conclusion, the view expressed by Yuravitch is accurate. The UK constitution does not conform to Montesquieu’s theory of a strict separation of powers and personnel. The significant fusion between the executive and the legislature remains the most prominent feature of the UK’s system of government. However, to state that the UK simply rejects the doctrine would be an oversimplification. As this essay has shown, each relationship between the branches of government is governed by a complex and evolving system of checks and balances designed to prevent the abuse of power. The legislative holds the executive to account, the judiciary can review executive actions, and Parliament remains sovereign over judicial law-making. The Constitutional Reform Act 2005 marked a significant step towards a clearer separation, particularly by establishing an independent judiciary and Supreme Court. Therefore, while the UK does not follow Montesquieu's "impractical" template, it has a more flexible and pragmatic constitution that embraces partial separation and interdependence between the branches. This system of checks and balances, rather than a pure separation, is the UK's primary mechanism for protecting liberty and upholding the rule of law.
References
Bagehot, W. (1867) The English Constitution. Chapman and Hall.
Bradley, A., Ewing, K. and Knight, C. (2018) Constitutional and Administrative Law. 17th ed. Pearson.
Hailsham, Lord. (1976) ‘Elective Dictatorship’. The Listener, 21 October 1976.
Montesquieu, C. (1748) De l'Esprit des Loix (The Spirit of the Laws).
Yuravitch, D. (2024) Public Law: Principles to Practice. 1st ed. OUP.
Legislation
Constitutional Reform Act 2005
House of Commons Disqualification Act 1975
Human Rights Act 1998
War Damage Act 1965
Cases
Burmah Oil Co Ltd v Lord Advocate [1965] AC 75
Council of Civil Service Unions v Minister for the Civil Service [1985] 3 All ER 935
R (Miller) v The Prime Minister [2019] UKSC 41
