Royal prerogative

The royal prerogative comprises residual common-law powers vested in the Crown, exercisable by ministers without statutory authority. It covers foreign affairs, defence, honours, mercy, and certain parliamentary functions. Three fundamental rules govern it: (1) statute always prevails over prerogative—where they overlap, prerogative falls into abeyance (De Keyser); (2) the executive cannot create new prerogatives or use existing ones to alter domestic law or remove statutory rights (BBC v Johns, Miller I); (3) prerogative exercises are justiciable on public law grounds unless no legal standards exist (GCHQ, Miller II). The rationale is constitutional balance: preserving necessary executive flexibility while subjecting it to legal limits that protect parliamentary sovereignty and the rule of law.

Attorney-General v De Keyser's Royal Hotel Ltd [1920] AC 508: Where statute covers the same ground as prerogative, statute displaces prerogative entirely—the Crown cannot bypass statutory conditions by invoking common-law powers. This establishes the fundamental hierarchy between legislation and executive discretion.

Council of Civil Service Unions v Minister for the Civil Service [1985] AC 374: Prerogative powers are reviewable on grounds of illegality, irrationality, and procedural impropriety—the source of power is irrelevant to justiciability. This revolutionised administrative law by bringing the executive's most discretionary acts within judicial supervision.

R v Secretary of State for the Home Department, ex parte Fire Brigades Union [1995] 2 AC 513: Prerogative cannot frustrate parliamentary intention, even regarding uncommenced statutes—constitutional propriety requires executive powers be exercised compatibly with statutory purpose. This prevents tactical use of prerogative to undermine legislative policy.

R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5: Prerogative cannot remove statutory rights or change domestic law—triggering Article 50 required legislation because it would inevitably extinguish EU law rights. This reinforces that executive action operates within, not above, the statutory framework.

R (Miller) v The Prime Minister [2019] UKSC 41: The limits of prerogative powers are always justiciable; prorogation that frustrates Parliament without reasonable justification is unlawful. This represents the high-water mark of judicial control over executive discretion.

Courts apply a two-stage analysis. First: does the claimed prerogative exist? This is always a justiciable question of law—courts examine historical precedent and will not recognise novel powers (BBC v Johns). Second: was the exercise lawful? Post-GCHQ, apply standard judicial review grounds, considering whether legal standards exist for the particular subject-matter.

For statute/prerogative conflicts, identify any overlap in subject-matter. If statute regulates the field, prerogative cannot be used even if statute is more onerous (De Keyser) or not yet commenced (Fire Brigades Union). Where prerogative subsists, examine whether its exercise alters domestic law or removes rights (Miller I), frustrates constitutional functions (Miller II), or breaches procedural fairness/rationality (GCHQ).

Common triggers include: executive attempts to bypass Parliament (treaties pre-CRAG, Article 50), emergency action without statutory basis, use of archaic powers in modern contexts. Remember conventions constrain politically but not legally—distinguish careful between legal limits and political practice.

Confusing all executive action with prerogative: Most government activity is statutory. Prerogative is only the residual common-law power where statute is silent—precisely identify the source of power.

Overstating non-justiciability: Post-Miller II, almost nothing is wholly immune. The question is whether legal standards exist, not whether the topic is 'political'. Even foreign affairs and national security face legal limits.

Misreading De Keyser: Statute doesn't 'abolish' prerogative but places it in abeyance where they overlap. The prerogative may revive if statute is repealed (see Dissolution and Calling of Parliament Act 2022).