Sources of the UK Constitution (3) – The Royal Prerogative & Constitutional Conventions

The Royal Prerogative and Constitutional Conventions

The United Kingdom's unwritten constitution draws upon several distinct sources of law. Earlier materials in this series examined Acts of Parliament and case law as primary sources. This article turns to two further sources that are essential to understanding how the British constitutional order actually functions in practice: the Royal Prerogative and constitutional conventions. Though they differ fundamentally in their legal character, both shape the daily exercise of governmental power and the relationship between the Crown, Parliament, and the judiciary.

The Royal Prerogative

Definition and Historical Background

The Royal Prerogative refers to those residual powers and privileges that were once exercised by the monarch as absolute ruler and which have not been removed by Parliament. Historically, the sovereign held sweeping executive authority — the power to wage war, conclude treaties, summon and dissolve Parliament, and govern the realm without legislative interference. Over the centuries, however, Parliament progressively curtailed these powers, either by statute or through the development of constitutional conventions that constrain how and by whom the powers are exercised.

The prerogative is therefore best understood as what remains of original monarchical authority after centuries of parliamentary encroachment. It is not a power created by Parliament; rather, it survives only because Parliament has not yet chosen to abolish it. As a matter of constitutional principle, where Parliament legislates in an area previously governed by prerogative, the statute displaces the prerogative to the extent of any inconsistency.

The Impact of the Crown Proceedings Act 1947

One of the most significant statutory inroads into the prerogative was made by the Crown Proceedings Act 1947. Before its enactment, the Crown enjoyed immunity from civil suits in tort and contract, meaning that individuals who suffered wrongs at the hands of government had extremely limited recourse. The Crown Proceedings Act 1947 abolished this immunity, making the Crown liable in tort and contract in broadly the same manner as a private individual or company. This reform removed a substantial portion of the practical advantage the Crown had previously enjoyed, and it remains one of the clearest examples of Parliament using legislation to circumscribe prerogative privilege.

The Scope of Remaining Royal Prerogative Powers

Despite successive statutory reductions, a meaningful body of prerogative power survives. These remaining powers fall into two broad categories: those concerning foreign affairs and those concerning domestic governance.

Foreign Affairs Powers

In the field of external relations, the Crown retains prerogative authority to:

• declare war and deploy armed forces abroad;
• conclude and ratify treaties with foreign states; and
• recognise foreign states and governments.

These powers are significant because they remain largely unreviewable by the courts in their political dimension, though the courts have in recent years shown a willingness to review whether the prerogative power claimed actually exists and, if so, whether its exercise is lawful.

Domestic Affairs Powers

On the domestic front, the surviving prerogative includes authority to:

• summon, prorogue, and dissolve Parliament (though dissolution is now substantially regulated by statute);
• appoint and dismiss the Prime Minister and other ministers;
• grant Royal Assent to Bills passed by Parliament;
• deploy armed forces within the United Kingdom for the defence of the realm;
• exercise the prerogative of mercy — granting pardons or commuting sentences; and
• confer public honours, such as peerages and appointments to the Order of the British Empire.

The Exercise of Prerogative in Practice: Exercise by the Prime Minister and Cabinet

Although these powers formally remain vested in the Crown, constitutional convention has long dictated that the vast majority of them are exercised in practice by the Prime Minister and Cabinet acting in the monarch's name. The sovereign acts on ministerial advice, and in almost all circumstances is constitutionally expected to follow that advice. The practical effect is that prerogative powers are wielded by democratically accountable ministers rather than by an unelected head of state, thereby reconciling the formal legal position with democratic principles.

This distinction between the formal legal holder of a power and its practical exerciser is one of the defining features of the British constitution. It illustrates the intimate relationship between the Royal Prerogative and constitutional conventions: the prerogative provides the legal authority, while conventions determine how and by whom it is actually used.

Limits on the Prerogative: The Miller Litigation

The most significant modern judicial statement on the limits of prerogative power came in R (Miller) v Secretary of State for Exiting the European Union [2017]. The Supreme Court held that the Government could not use prerogative powers to trigger Article 50 of the Treaty on European Union — the formal notification of the United Kingdom's intention to withdraw from the EU — without prior authorisation from Parliament by way of primary legislation.

The Court reasoned that EU law had been incorporated into domestic law by the European Communities Act 1972, and that using the prerogative to withdraw from the EU would inevitably remove rights that Parliament had conferred on individuals through that statute. Because the prerogative cannot be used to alter, curtail, or remove rights established by Act of Parliament, the triggering of Article 50 required parliamentary authority. The decision represents a powerful affirmation of the principle that prerogative powers, however wide, cannot override parliamentary sovereignty.

Constitutional Conventions

Definition and Character: Binding but Not Enforceable

Constitutional conventions are non-legal rules of constitutional behaviour that are binding in the sense that significant political consequences follow from their breach, but which are not enforceable by the courts in the manner of legal rules. They represent the informal, practice-based dimension of the UK constitution — the unwritten understandings about how constitutional actors ought to behave.

Because conventions are non-legal in character, their creation requires no special procedure or legislative formality. They can emerge gradually from consistent practice, from express agreements between constitutional actors, or from the logic of constitutional principle. This informality is at once their greatest strength and the source of periodic criticism: it makes conventions highly adaptable to changing political circumstances, but it also means their precise content can be disputed.

The Roles of Constitutional Conventions

Constitutional conventions perform four important functions within the UK constitutional order:

1. Limiting the monarch's extensive legal powers without requiring wholesale statutory reform. Many prerogative powers remain legally available to the Crown but are constrained by convention from being exercised in ways that would be constitutionally inappropriate.

2. Enabling the effective and flexible operation of the constitution and government. Because conventions need not be reduced to statute, they can evolve organically to meet new challenges without the cumbersome process of legislation.

3. Ensuring governmental accountability to Parliament. Conventions such as individual ministerial responsibility and collective Cabinet responsibility oblige ministers to answer to Parliament for their conduct and that of their departments.

4. Maintaining the separation of powers between the different organs of the state. Conventions governing the relationship between the judiciary, the executive, and the legislature help to preserve institutional independence and prevent inappropriate concentrations of power.

Principal Examples of Constitutional Conventions

The following table sets out the principal constitutional conventions that govern the operation of the UK constitution:

The Attitude of the Courts: Recognition Without Enforcement

The courts occupy a nuanced position in relation to constitutional conventions. They are willing to recognise that a convention exists and to take it into account in interpreting the legal position, but they will not enforce a convention as though it were a rule of law. The principal reason for this judicial restraint is that conventions exist precisely to govern sensitive political situations that are not well suited to resolution by litigation. To enforce conventions as legal rules would risk drawing the courts into highly partisan political disputes and would undermine the flexibility that makes conventions valuable.

Two cases illustrate this judicial approach with particular clarity.

In Madzimbamuto v Lardner-Burke [1969], arising from the Rhodesian Unilateral Declaration of Independence, the Privy Council declined to hold that a constitutional convention prevented the Westminster Parliament from legislating for a territory even against the wishes of its government. The courts confirmed that legislation contrary to an established convention was legally valid, and they refused to enforce the convention as a bar to the exercise of parliamentary sovereignty. The case demonstrates that, however strong a convention may be in political terms, it does not constrain what Parliament may legally enact.

In A-G v Jonathan Cape [1976], the court was asked to restrain publication of the diaries of a former Cabinet minister on the ground that Cabinet collective responsibility required the confidentiality of Cabinet discussions. The court acknowledged the existence of the convention requiring Cabinet confidentiality, but it refused to grant an injunction solely on the basis that the convention had been broken. The court treated the matter through the lens of the equitable law of confidence rather than as a constitutional convention to be enforced directly. The case confirms that the mere recognition of a convention's existence by the courts does not translate into legal enforceability.

The Codification Debate: Preserving Flexibility

A recurring theme in constitutional scholarship is the argument that conventions should be codified — written down and given legal force in the manner of a constitutional statute. Proponents of codification argue that it would enhance legal certainty and democratic accountability by making the rules of constitutional behaviour clear and enforceable.

However, there are compelling reasons for caution. If conventions were given the same legal status as Acts of Parliament, they would lose the very quality that makes them constitutionally valuable: their flexibility. Conventions can evolve to accommodate new political realities without recourse to formal amendment procedures. If they were treated as fixed legal rules, the constitution would become rigid, and the inability to adapt conventions in a timely fashion to novel circumstances could generate genuine constitutional crises. The consensus among most constitutional scholars is that the unwritten, political character of conventions is a feature rather than a flaw of the British constitutional system.

Conclusion: The Interaction of Royal Prerogative and Constitutional Conventions

The Royal Prerogative and constitutional conventions are distinct legal phenomena, but they are deeply interdependent. The prerogative defines what formal legal powers the Crown holds; conventions determine how, when, and by whom those powers are exercised in practice. Together, they constitute a system of informal but effective constitutional governance that has evolved over centuries to balance legal authority with political accountability.

The prerogative provides the formal legal basis for significant executive action — from declaring war to appointing a Prime Minister — while conventions ensure that these powers are exercised in a manner consistent with democratic principles and parliamentary sovereignty. Where the prerogative conflicts with parliamentary authority, as R (Miller) v Secretary of State for Exiting the European Union [2017] made clear, it is Parliament that prevails. Where conventions are breached, political consequences — resignation, loss of confidence, electoral defeat — rather than legal sanctions follow.

Understanding this interplay is essential for any student of English public law. The UK constitution is not a single document but a living system of interlocking sources, and the Royal Prerogative and constitutional conventions lie at its very heart.