# The royal prerogative

> **Key takeaway:** Residual common-law Crown powers, mostly ministerial. Existence/extent: law for courts. Statute displaces (De Keyser). Reviewable in principle (CCSU). Miller cases on modern limits. Not a blank cheque.

- **Jurisdiction:** England & Wales
- **Practice area:** Public Law
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/PublicLaw/royal-prerogative
- **Keywords:** royal prerogative, De Keyser, CCSU, Case of Proclamations, Miller, executive power, justiciability, prerogative powers

## What is this about?

The royal prerogative comprises residual common-law powers of the Crown recognised by the courts, now largely exercised by ministers. It covers areas such as foreign affairs, defence, mercy, and certain honours/appointments — but is excluded or displaced where statute occupies the field.

## What is the core rule?

Prerogative powers exist only as the common law allows; their existence and extent are questions of law for the courts (Case of Proclamations lineage; modern restatement in cases such as BBC v Johns themes and CCSU). Where a statute regulates a field, the prerogative may be displaced (De Keyser). Exercise of prerogative is in principle reviewable on ordinary public-law grounds, though some national-security/foreign-affairs contexts remain non-justiciable or lightly reviewed (CCSU). Prorogation and treaty-related steps have been intensively litigated in the Miller cases.

## What are the elements or test?

1. Does a claimed prerogative power exist as a matter of law?
2. Has statute abridged or replaced it (De Keyser)?
3. Who may exercise it (ministers; order in council)?
4. Is the particular exercise justiciable?
5. Standard JR grounds if justiciable

## Which authorities matter?

- **Case of Proclamations (1611) 12 Co Rep 74** — Historic limit: the King cannot by proclamation change the law or create new offences.
- **Attorney-General v De Keyser's Royal Hotel Ltd [1920] AC 508** — Statute covering the same ground suspends or ousts inconsistent prerogative use.
- **Council of Civil Service Unions v Minister for the Civil Service [1985] AC 374** — Prerogative reviewable in principle; national security may limit intensity/justiciability.
- **R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5; R (Miller) v Prime Minister [2019] UKSC 41** — Modern landmarks on prerogative, statute, and parliamentary accountability.

## How does this apply in practice?

Always search for a statutory scheme before relying on prerogative. Treat 'foreign affairs' as a label, not an automatic immunity. Pair with sovereignty and separation notes.

## What are common pitfalls?

- Assuming prerogative is unlimited residual power
- Ignoring De Keyser displacement by statute
- Treating all prerogative acts as non-justiciable
- Confusing prerogative with statutory executive powers

## When would a practitioner use this?

JR of ministerial decisions claimed under prerogative; advice on treaty and defence-related powers.

## Quick reference

Residual common-law Crown powers, mostly ministerial. Existence/extent: law for courts. Statute displaces (De Keyser). Reviewable in principle (CCSU). Miller cases on modern limits. Not a blank cheque.

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*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*