Royal prerogative and Miller (Nos 1 and 2)

The royal prerogative is the residue of legal authority left to the Crown, exercised in modern conditions almost always by ministers. Its constitutional importance lies not in antiquarian monarchy but in executive government: treaty-making, foreign affairs, defence, passports, public appointments, honours, mercy, prorogation and dissolution have all been associated with prerogative authority. The central question for public lawyers is therefore not whether the Crown has prerogatives, but how far ministers may use non-statutory powers consistently with parliamentary sovereignty, the rule of law, and judicial review.

This week joins the first five weeks of Durham Constitutional Law. Week 1 supplies the point that the constitution is plural in source: statute, common law, convention, principle and practice interact. Week 2 matters because prerogative cannot alter the legal supremacy of Parliament. Week 3 matters because constitutional statutes are not displaced casually; Miller No 1 is unintelligible without the idea that the European Communities Act 1972 created a constitutional scheme of domestic rights. Week 4 matters because the rule of law requires legal limits on public power, including power claimed from the prerogative. Week 5 matters because the Miller litigation was not merely about outcomes; it was about the institutional boundary between executive choice, parliamentary control and judicial adjudication.

The doctrine has two recurrent propositions. First, the existence and extent of a prerogative power are questions of law for the courts. Secondly, where a prerogative exists, some exercises of it are reviewable, although intensity of review varies with subject matter. Foreign affairs and national security are not legal black holes, but courts often recognise institutional limits when the issue requires political, diplomatic or military judgment. Miller No 2 confirms that even a high constitutional prerogative, prorogation, may be subject to legal limits where it affects Parliament’s capacity to legislate and scrutinise government.

Miller No 1 and Miller No 2 should not be revised as free-standing Brexit stories. They are doctrinally different. Miller No 1 concerned whether ministers could use the foreign affairs prerogative to give Article 50 notice without statutory authorisation. The Supreme Court held that they could not, because withdrawal would change domestic law and remove rights created by statute. Miller No 2 concerned whether advice to prorogue Parliament was justiciable and lawful. The Supreme Court held that it was justiciable and unlawful because it frustrated Parliament’s constitutional functions without reasonable justification.

For Durham assessment, the best answers avoid sloganising either case. Do not write simply that courts stopped Brexit, or that courts now review all prerogative powers. The correct account is more precise: prerogative powers are legally recognised by the common law; they are displaced or controlled by statute; they cannot be used to change domestic law without parliamentary authority; and their exercise is reviewable where legal standards can be articulated, especially where fundamental constitutional principles are impaired.

The modern prerogative is a legal remnant of monarchical power. Historically, the Crown possessed extensive powers of government: making war and peace, conducting foreign relations, summoning and dissolving Parliament, administering justice, granting charters and regulating trade. The constitutional settlement of the seventeenth century did not abolish the Crown, but it denied unilateral law-making and taxation. The Case of Proclamations established the enduring common law proposition that the King could not create offences or alter the law by proclamation. The Bill of Rights 1688 condemned the suspending of laws by royal authority without parliamentary consent. These materials explain why prerogative is best understood negatively: it is not a source of legislative supremacy, but a set of executive powers recognised only so far as law permits.

The gradual movement from personal monarchy to responsible government changed the identity of the actor without removing the legal category. The sovereign formally acts, but constitutional convention normally requires action on ministerial advice. Thus prerogative today is principally a power of the executive. This matters because ministerial use of prerogative can bypass ordinary legislative procedure unless law or political convention requires parliamentary involvement. Treaty-making is the classic example. At common law, making and unmaking treaties is a prerogative function because treaties operate internationally. But if treaty action alters domestic law or domestic rights, parliamentary legislation is required. This distinction between international and domestic legal effect is the hinge of Miller No 1.

The twentieth century added a second dimension: the growth of the administrative state and judicial review. In Attorney General v De Keyser’s Royal Hotel, the House of Lords held that where statute covers the ground, ministers cannot choose the prerogative in order to avoid statutory limits or compensation. In Laker Airways and Fire Brigades Union, courts policed executive reliance on prerogative where its use undermined a statutory scheme or frustrated Parliament’s intention. In CCSU, the House of Lords rejected the old view that prerogative source alone excluded review. The question became the subject matter and legal suitability of review, not merely the formal source of power.

This history is often compressed into three stages. The first is denial of prerogative legislation: the executive cannot change law by unilateral command. The second is statutory priority: where Parliament has legislated, prerogative yields or is placed in abeyance. The third is reviewability: exercises of prerogative may be judicially reviewed where the court can apply legal standards. Miller No 1 stands mainly in the first and second stages; Miller No 2 stands mainly in the third, though it also depends on parliamentary sovereignty and accountability.

The Brexit context sharpened these old propositions. Article 50 notification was formally an international act. Yet withdrawal from the European Union would inevitably affect domestic rights because the European Communities Act 1972 was the statutory conduit through which EU law took effect in UK law. Prorogation was formally a prerogative proceeding in Parliament. Yet a long prorogation at a moment of constitutional importance prevented Parliament from legislating or scrutinising ministers. The constitutional novelty of Miller lies less in the principles asserted than in their application to politically acute facts.

1. The prerogative is a common law category. Dicey’s familiar definition describes the prerogative as the residue of discretionary or arbitrary authority legally left in the hands of the Crown. The definition is useful but incomplete. It emphasises residual authority, but modern law treats the prerogative not as arbitrary in the pejorative sense but as legally bounded executive power. The Crown has only those prerogatives recognised by law. Courts determine whether a claimed prerogative exists and what its legal limits are.

1. The executive cannot change domestic law by prerogative. This is the deepest principle in the field. The Crown may conduct international relations, but it cannot legislate for the United Kingdom. A treaty does not alter domestic law unless incorporated by Parliament. Equally, ministers cannot use prerogative to remove statutory rights, suspend statutory duties, or empty a statutory scheme of practical operation. Miller No 1 is an application of this proposition: Article 50 notification would lead to withdrawal from the EU Treaties and thereby remove a source of domestic law and rights created through the European Communities Act 1972. That required statutory authorisation.

1. Statute prevails over prerogative. If Parliament has legislated in a field, ministers cannot rely on a parallel prerogative to escape statutory conditions. De Keyser’s Royal Hotel is the foundation. The prerogative is not necessarily abolished; it may be displaced or placed in abeyance for so long as the statutory regime governs the field. The practical consequence is that a public lawyer must always ask whether a statute covers the ground. Where statute is exhaustive, prerogative cannot be used inconsistently with it. Where statute assumes the continued existence of the prerogative, the issue is one of construction.

The leading cases show a steady judicial movement from defining prerogative limits to reviewing prerogative exercises. The Case of Proclamations remains the canonical authority that the Crown cannot create law by prerogative. It is not a modern judicial review case, but it supplies the basic legality condition: prerogative exists only where the law recognises it.

Attorney General v De Keyser’s Royal Hotel is the key statutory-priority case. During wartime the Crown requisitioned a hotel. Statute provided a compensation code. The Government could not rely on prerogative to avoid statutory compensation. The case is fundamental because it prevents ministerial choice between law-constrained statutory powers and less constrained prerogative powers. If Parliament has legislated, that scheme governs.

Laker Airways and Fire Brigades Union develop the anti-frustration principle. In Laker, the executive could not use prerogative foreign affairs powers in a way that defeated statutory licensing rights. In Fire Brigades Union, the Home Secretary could not use prerogative power to introduce a tariff scheme when Parliament had enacted, though not commenced, a statutory criminal injuries scheme. The majority’s reasoning illustrates that executive inaction or alternative action may unlawfully frustrate Parliament’s legislative intention.

CCSU is the standard justiciability authority. The case concerned a ban on trade union membership at GCHQ, imposed under prerogative authority. The House of Lords accepted that prerogative powers are not immune merely because their source is non-statutory. However, national security made the particular decision unsuitable for ordinary review. CCSU is therefore both a liberalising and a restraining case: source does not bar review, but subject matter may limit it.

Miller No 1 is the leading modern case on prerogative and statutory rights. The Government argued that Article 50 notification was an exercise of the foreign affairs prerogative. The majority accepted that making and unmaking treaties is ordinarily prerogative, but held that notification would change domestic law because EU law had domestic force under the 1972 Act. That could not be done without statute. The dissenting justices viewed the 1972 Act as ambulatory: it gave effect to EU law only so long as the UK remained party to the Treaties, and did not restrict withdrawal.

Miller No 2 is the leading modern case on prorogation. The Supreme Court held unanimously that the question was justiciable and that the advice to prorogue was unlawful. The legal limit was framed by two constitutional principles: parliamentary sovereignty and parliamentary accountability. A prorogation which frustrates or prevents Parliament from carrying out its constitutional functions, without reasonable justification, is unlawful. The prorogation was exceptionally long, occurred at a moment when Parliament had a vital role in scrutinising Brexit, and no reasonable justification had been put forward.

Together the cases form a usable doctrinal ladder: no prerogative law-making; no prerogative override of statute; no prerogative frustration of statutory schemes; reviewability depends on legal standards and subject matter; and high constitutional prerogatives may be limited where they impair Parliament’s legislative and accountability functions.

See practice questions section below.

See further reading section below.