Royal prerogative and Miller (Nos 1 and 2)

This topic sits at the point where the abstract themes of the first five weeks become operational. Parliamentary sovereignty, constitutional statutes, the rule of law, and separation of powers are not merely descriptive labels. They determine when the executive may act without Parliament; when prerogative power is displaced or limited by statute; when the courts will decide questions touching high politics; and how the legal constitution responds when government invokes ancient powers for modern constitutional purposes.

The royal prerogative is the residue of legal authority left in the Crown, now exercised by ministers, without the need for statutory authorisation. It includes important powers in foreign affairs, defence, passports, mercy, honours, public appointments, the making and unmaking of treaties, and the summoning, proroguing and dissolving of Parliament. But its legal status is sharply limited. The prerogative is not a general power to govern. It is not a power to change domestic law. It cannot override statute. Its existence and extent are matters for the courts. Its exercise may be reviewable, depending on the subject matter and the legal standard invoked.

The two Miller cases are therefore best understood not as isolated Brexit cases, but as modern restatements of older constitutional principles. In Miller No 1, the Supreme Court held that ministers could not use the foreign affairs prerogative to give notice under Article 50 TEU because doing so would inevitably lead to changes in domestic law and the loss of rights created by the European Communities Act 1972. An Act of Parliament was required. The case is about the relationship between prerogative and statute, and about the constitutional status of statutory rights.

In Miller No 2, decided with Cherry, the Supreme Court held that the Prime Minister's advice to prorogue Parliament for five weeks in 2019 was justiciable and unlawful. The relevant prerogative power existed, but its lawful limits were fixed by constitutional principles: parliamentary sovereignty and parliamentary accountability. A prorogation which has the effect of frustrating or preventing Parliament from performing its constitutional functions, without reasonable justification, is unlawful. The prorogation was void.

For Tripos purposes, the central task is not to praise or denounce the outcomes. It is to identify the doctrinal path. Ask four questions in every prerogative problem. First, does the alleged prerogative exist, and what is its legal extent? Secondly, has statute displaced, regulated or implicitly limited it? Thirdly, would its use change domestic law, defeat statutory rights, or frustrate a statutory scheme? Fourthly, is the issue justiciable, and if so what standard of review applies? Good answers show how those questions connect the Case of Proclamations, De Keyser, CCSU, Fire Brigades Union, Bancoult, Miller No 1 and Miller No 2 into a single line of constitutional reasoning.

The royal prerogative originated in monarchical government. It described those powers which belonged to the Crown by virtue of the Crown's common law authority, rather than by grant of Parliament. Historically, prerogative power was inseparable from political conflict: taxation, standing armies, dispensing powers, foreign policy, and control over Parliament. The constitutional settlement after the seventeenth century did not abolish the prerogative. It juridified it. The monarch could no longer claim legally unlimited authority; prerogative powers became powers recognised, defined and limited by law.

The orthodox starting point is the Case of Proclamations. The Crown could not by proclamation create new offences, alter the common law, or suspend statutes. The significance of the case is not merely historical. It establishes two propositions which remain central. First, the courts decide whether a prerogative exists. Secondly, the prerogative cannot change the law of the land. That second proposition is the direct ancestor of Miller No 1.

The Bill of Rights 1688 then gave political and statutory form to the rejection of dispensing and suspending powers. It declared illegal the pretended power of suspending laws or their execution by royal authority without Parliament. This did not mean every prerogative power was suspect. It meant that where Parliament had legislated, ministers could not use prerogative authority to set the legislation aside.

The nineteenth and early twentieth centuries saw the practical transformation of the prerogative. The monarch's personal discretion gave way to ministerial advice and ministerial responsibility. The prerogative became, in Diceyan terms, part of the legal powers of the executive, but politically controlled by Parliament. That settlement depended on assumptions: that government would be accountable to the House of Commons; that Parliament could legislate to control abuse; and that courts would police legal limits without entering forbidden political territory.

De Keyser's Royal Hotel is the classic twentieth-century authority on the interaction between statute and prerogative. Where statute covers the same ground as a prerogative power, ministers must proceed under the statute and accept its conditions, including compensation requirements. The case is often described as a displacement doctrine: statute does not necessarily abolish the prerogative, but it puts it into abeyance so far as Parliament has regulated the field. Fire Brigades Union later extended the concern from direct inconsistency to frustration of a statutory scheme not yet fully brought into force.

The modern administrative state posed a different question: even if a prerogative power exists and is not displaced by statute, can its exercise be judicially reviewed? CCSU answered yes in principle. The source of power is not decisive; the subject matter may be. Some prerogatives, such as national security, treaty-making, or the deployment of armed forces, may involve issues unsuited to judicial determination. But prerogative power is not immune merely because it is prerogative.

Miller No 1 and Miller No 2 must be located against that history. Miller No 1 treated Article 50 notification as formally an act in foreign relations but substantively an act with unavoidable domestic legal consequences. Miller No 2 treated prorogation as politically sensitive but legally bounded where its effect was to disable Parliament's constitutional functions. Both cases reasserted an old proposition in modern conditions: executive power is legally constituted power, and legality is ultimately for courts to determine.

1. The prerogative is residual legal power, not inherent executive sovereignty. The executive does not possess a free-standing power to act whenever statute is silent. A prerogative must be identified as a recognised common law power. The courts determine its existence and extent. This matters in problem questions: do not begin by asking whether the action is politically desirable; begin by asking what legal power authorises it.

1. The prerogative cannot alter domestic law. This is the central principle from the Case of Proclamations and Miller No 1. Ministers may act internationally under the treaty prerogative, but they cannot, by that act alone, change domestic legal rights and duties. The United Kingdom's dualist constitution is crucial. Treaties are made and unmade by ministers on the international plane. They do not alter domestic law unless Parliament incorporates them. Conversely, where Parliament has incorporated treaty-derived rights into domestic law, ministers cannot remove those rights by prerogative action unless Parliament has authorised that result.

1. Statute prevails over prerogative. This has several forms. An express statutory provision may abolish or regulate a prerogative. A statute may cover the same field and thereby require ministers to use statutory powers rather than prerogative powers, as in De Keyser. A statutory scheme may be frustrated by prerogative action, even where there is no direct textual contradiction, as in Fire Brigades Union. The stronger the statutory scheme, the harder it is for ministers to rely on residual prerogative authority.

1. Constitutional statutes affect the analysis. Week 3 should now be brought into the answer. The European Communities Act 1972 was not an ordinary statute. It created a conduit through which EU law rights became domestic legal rights. Miller No 1 relied not only on the general priority of statute over prerogative, but also on the constitutional character of the 1972 Act. If Parliament has created a major constitutional regime, the courts will be slow to infer that ministers may dismantle it using prerogative authority.

The development begins with the Case of Proclamations, where the judges rejected the idea that royal proclamations could change law. It remains the canonical authority for the proposition that prerogative power exists only to the extent recognised by law. It is easy to cite as a slogan; better answers explain why it matters. The case makes the courts guardians of the legal boundary of executive power.

De Keyser supplies the next essential step. During wartime, the Crown requisitioned property and sought to rely on prerogative power rather than statutory powers which carried compensation. The House of Lords held that where Parliament had legislated for the same subject matter, ministers had to use the statutory scheme. The point is not that the prerogative evaporates for all purposes. Rather, it cannot be used to evade statutory conditions.

Laker Airways illustrates another aspect of the same discipline. The Crown could not use treaty and foreign affairs powers to defeat statutory rights granted under aviation legislation. This case is particularly useful for essays on foreign affairs because it undermines any suggestion that external relations are wholly insulated from domestic legal control.

CCSU modernised reviewability. The House of Lords held that a decision under prerogative power was not immune merely because of its source. The result turned on national security, which made the particular decision unsuitable for review. But the doctrinal move was decisive: prerogative power became part of administrative law's general field, subject to limits of justiciability.

Fire Brigades Union concerned a ministerial decision to introduce a non-statutory compensation scheme instead of bringing into force a statutory scheme enacted by Parliament. The majority treated this as an unlawful frustration of Parliament's will. The case is important because it shows that prerogative or non-statutory powers may be unlawful even without direct contradiction of an operative statutory duty.

Bancoult (No 2) confirmed that prerogative legislation, in that case Orders in Council for a colony, could be reviewed by courts, while also showing the continuing weight of subject matter. The majority was deferential where security and overseas territory governance were concerned.

Miller No 1 and Miller No 2 are the modern capstones. Miller No 1 turned on domestic legal consequences and statutory rights. Miller No 2 turned on constitutional limits to prorogation and judicial capacity to enforce them. Together they show that prerogative power remains constitutionally important but legally subordinate: subordinate to statute, to domestic legal rights, and to fundamental constitutional principles where those principles generate legal limits.

See practice questions section below.

See further reading section below.