Separation between the Executive and the Judiciary
The relationship between the executive and the judiciary in English constitutional law is defined by a tension between the need for governmental effectiveness and the imperative of judicial independence. Unlike the legislature, which is subject to regular democratic scrutiny, and unlike the executive, which retains broad prerogative and statutory powers, the judiciary occupies a constitutionally distinct position: its function is to adjudicate upon the law impartially and without interference. This section examines how that separation is maintained, where it has historically broken down, and the mechanisms by which checks and balances are preserved.
Judicial Independence
Judicial independence requires that judges be free from pressure or interference from the executive when determining cases. In the United Kingdom, this principle is secured through a combination of common law tradition and statutory protection.
Historically, judges held their office at the pleasure of the Crown, which made them vulnerable to removal by the executive. The Act of Settlement 1701 addressed this problem by providing that judges hold office during good behaviour, meaning they can only be removed by a formal address from both Houses of Parliament. This security of tenure insulates judges from executive pressure and is a foundational element of judicial independence.
Financial independence is equally important. Judicial salaries are charged to the Consolidated Fund rather than being subject to annual parliamentary appropriation, which means the executive cannot use the threat of salary reduction as a form of pressure on the judiciary.
The Senior Courts Act 1981 reinforces these protections at a statutory level, and the Contempt of Court Act 1981 provides mechanisms to protect the integrity of judicial proceedings from external interference, including improper executive comment on pending cases.
The Role of the Constitutional Reform Act 2005
The most significant structural reform to the relationship between the executive and the judiciary in modern times was introduced by the Constitutional Reform Act 2005. Prior to this Act, the Lord Chancellor — a Cabinet Minister and member of the executive — simultaneously held judicial office as head of the judiciary, presided over the House of Lords in its legislative capacity, and was responsible for court administration. This concentration of roles in a single politically appointed figure was a conspicuous departure from the ideal of separation of powers.
The Constitutional Reform Act 2005 restructured these arrangements in three principal ways.
First, it created the UK Supreme Court to replace the Judicial Committee of the House of Lords as the final court of appeal. Previously, the Law Lords — the Lords of Appeal in Ordinary — sat as both legislators in the upper chamber and as the country's highest judicial tribunal. The Supreme Court, which came into existence in October 2009, is physically and institutionally separate from Parliament, thereby removing the most visible overlap between the legislature and the senior judiciary.
Second, the Act reformed the office of Lord Chancellor. The Lord Chancellor is no longer required to be a lawyer or a peer, and the judicial functions previously attached to the office have been largely transferred. Crucially, s 3 Constitutional Reform Act 2005 imposes an express statutory duty on the government — and in particular on Ministers — to uphold the independence of the judiciary. Ministers are prohibited from seeking to influence particular judicial decisions through any form of special access to the judiciary. This provision gives statutory expression to a constitutional convention that had previously operated informally.
Third, the Act established the Judicial Appointments Commission (JAC), an independent body responsible for selecting candidates for judicial appointment. Before the Act, senior judicial appointments were made by the Lord Chancellor acting on behalf of the Crown — a process that was opaque and potentially susceptible to executive patronage. Under the reformed system, appointments to fill vacancies in the Supreme Court are made by the Crown on the advice of the Prime Minister, who will have received a recommendation from the Lord Chancellor. The members of the Supreme Court and the JAC select from the recommendations, and the selection must be based solely on merit. This process substantially reduces the scope for executive influence over judicial appointments.
The Lords Justices of Appeal and puisne judges of the High Court are similarly appointed through the JAC process, reinforcing merit-based selection across the senior judiciary.
Overlap between the Executive and the Judiciary
Quasi-Judicial Functions and Challenges after the Human Rights Act 1998
Notwithstanding the reforms introduced by the Constitutional Reform Act 2005, a degree of overlap between the executive and judicial functions has persisted throughout English constitutional history and continues to exist. Prior to 2005, the Lord Chancellor's combined roles epitomised this overlap, but the problem was not confined to that office alone.
The Human Rights Act 1998 brought the rights guaranteed under the European Convention on Human Rights into domestic law and sharpened the constitutional tension between executive power and judicial scrutiny. A particularly prominent example is the Belmarsh Case [2004] in which the House of Lords held that the indefinite detention of foreign nationals under the Anti-terrorism, Crime and Security Act 2001 was incompatible with Articles 5 and 14 of the European Convention on Human Rights. The case illustrated both the willingness of the senior judiciary to scrutinise executive action in the field of national security and the limits of parliamentary authorisation as a justification for incompatible measures. The government's response — replacing indefinite detention with control orders — demonstrated how judicial declarations of incompatibility can prompt legislative and executive reform even without the formal power to strike down primary legislation.
Separately, R (Anderson) v Secretary of State for the Home Department [2002] concerned the power of the Home Secretary to set the tariff — the minimum period to be served — for mandatory life sentence prisoners. The House of Lords held that this power was incompatible with Article 6 of the European Convention on Human Rights, since the tariff-setting function is inherently judicial and must be exercised by an independent tribunal rather than a government Minister.
Areas where Executive Quasi-Judicial Functions Continue
Despite these developments, the executive retains quasi-judicial functions in two important areas.
The first is Administrative Tribunals. Tribunals exercise a judicial function in resolving disputes between individuals and the state (and sometimes between private parties), but they are frequently constituted with members drawn from, or appointed by, the executive. Although the Tribunals, Courts and Enforcement Act 2007 created a more unified and independent tribunal structure, the boundary between executive administration and judicial determination remains a live issue in this context.
The second is Compulsory Purchase Orders. When the government proposes to acquire land compulsorily — for example, to construct a new road or railway — the decision as to which land is to be acquired is quasi-judicial in nature, since it affects private rights and must follow statutory procedures. However, this decision is ultimately taken by the relevant government Minister rather than by an independent court. The affected landowner may challenge the legality of the order through the courts, but the substantive decision itself remains within the executive sphere.
Checks and Balances between the Executive and the Judiciary
The Importance of Judicial Independence
The separation of the judiciary from the executive serves a fundamental constitutional purpose: it enables an independent judiciary to review the actions of the executive and ensure that the executive does not exceed its powers or exercise them in an unlawful manner. In so doing, the judiciary upholds the rule of law.
In the United Kingdom, this function is of particular significance because Parliamentary scrutiny of the executive is not always effective. Where parliamentary oversight is limited — whether because of the executive's dominant position in the House of Commons through its majority, or because of the technical or covert nature of certain executive actions — an independent judiciary provides an alternative mechanism of accountability.
It must be acknowledged, however, that the position of the UK judiciary differs from that of constitutional courts in some other jurisdictions. As a consequence of operating within an unwritten constitution, the judiciary in the UK has no formal power to declare the actions of the executive, or legislation enacted by Parliament, to be unconstitutional in the sense of nullifying them entirely. In this respect, the UK differs from, for example, the Republic of Korea, whose Constitutional Court has the power to strike down legislation as unconstitutional under the Constitution of the Republic of Korea. In the UK, the principal remedy available to the judiciary in relation to Acts of Parliament is a declaration of incompatibility under s 4 Human Rights Act 1998, which does not affect the continuing validity of the legislation.
Judicial Review of Executive Action
Judicial review is the primary mechanism through which the judiciary exercises its supervisory jurisdiction over the executive. Through judicial review, the courts examine whether the executive has acted within the scope of its legal authority and in accordance with the requirements of procedural fairness and rationality.
Where the executive exercises powers derived from statute, the court ensures that those powers are exercised in accordance with the purpose for which Parliament conferred them and that they have not been exceeded or abused. Where the executive exercises powers derived from Royal Prerogative, judicial review determines the allowable extent of those powers and ensures that they are exercised appropriately.
A critical feature of judicial review is that the courts examine only the legality of executive decisions or actions — they do not examine the merits of those decisions. Whether a particular executive decision was wise, expedient, or in the public interest is a matter for the executive, not for the courts. The judiciary intervenes only where the decision is unlawful, irrational, or procedurally improper. This restraint reflects both the constitutional role of the executive as the branch responsible for government policy and the democratic legitimacy that the elected government possesses and that unelected judges do not.
Judicial Control of Royal Prerogative Powers
The Royal Prerogative comprises those residual common law powers exercisable by the Crown that have not been abrogated by statute. The courts have developed a body of doctrine governing the extent to which the exercise of prerogative powers is subject to judicial scrutiny.
Two foundational principles have been established by the courts. First, new prerogative powers cannot be created: Case of Proclamations (1610) established that the Crown cannot claim a prerogative power that has no basis in historical practice or legal authority. Second, the scope of existing prerogative powers cannot be extended: BBC v Johns [1965] confirmed that a prerogative power is fixed in its scope and cannot be stretched to cover new situations.
The leading modern authority is CCSU v Minister for Civil Service [1984], in which the House of Lords confirmed that the courts have jurisdiction to review the exercise of prerogative powers in principle. However, the House also identified a category of prerogative powers that are non-justiciable — that is, inappropriate for judicial review by reason of their subject matter. The non-justiciable areas identified in that case include: the making of international treaties, the control of the armed forces, the defence of the realm, the dissolution of Parliament, the prerogative of mercy, and the granting of public honours.
The Limits of Non-Justiciability
The category of non-justiciable prerogative powers is not entirely fixed. Courts have, over time, become willing to review the exercise of certain prerogative powers that were previously regarded as beyond scrutiny.
In Blackburn v Attorney-General [1971], the courts confirmed that the executive's exercise of the prerogative power to enter into international treaties is immune from judicial review, since treaty-making is a matter of foreign policy in which the courts will not intervene.
More recently, however, the courts have been willing to examine specific aspects of powers previously regarded as non-justiciable. In R (Bentley) v Secretary of State for the Home Department [1993], the courts began reviewing the exercise of the prerogative of mercy by the Home Secretary — a power that had been listed among the non-justiciable categories in CCSU v Minister for Civil Service [1984]. The court held that whilst the merits of the decision to exercise or refuse mercy were not reviewable, the procedural aspects of how the prerogative was exercised could be subject to scrutiny.
Similarly, in R (Everett) v Secretary of State for Foreign and Commonwealth Affairs [1989], the courts reviewed the Foreign Secretary's exercise of the power to issue passports — another prerogative function — and held it was, in principle, amenable to judicial review.
These developments illustrate a gradual expansion of the courts' willingness to scrutinise prerogative powers, driven in part by the growing influence of the Human Rights Act 1998 and the principle that executive action affecting individual rights should be open to legal challenge.
Nevertheless, the courts remain reluctant to review the exercise of prerogative powers in areas that are highly political in nature — particularly the conduct of foreign relations, national security, and the defence of the realm. In these domains, the courts recognise that they lack the institutional competence to second-guess executive judgement. As a consequence, some powers exercised by the executive have remained beyond the effective scrutiny of both the judiciary and the legislature, representing a genuine limitation on the principle of checks and balances as it operates in the UK constitutional order.