The royal prerogative is a body of customary authority, privilege, and immunity attached to the British monarch (or "sovereign"), recognised in the United Kingdom.

The monarch remains constitutionally empowered to exercise the royal prerogative against the advice of the prime minister or the cabinet, but in practice would likely only do so in emergencies or where existing precedent does not adequately apply to the circumstances in question.

Today, the royal prerogative is available in the conduct of the government of the United Kingdom, including foreign affairs, defence, and national security.

[1] A prominent constitutional theorist, A. V. Dicey, proposed in the nineteenth century that: The prerogative appears to be historically and as a matter of fact nothing else than the residue of discretionary or arbitrary authority which at any given time is legally left in the hands of the crown.

[2] While many commentators follow the Diceyan view, there are constitutional lawyers who prefer the definition given by William Blackstone in the 1760s:[3]By the word prerogative we usually understand that special pre-eminence which the King hath, over and above all other persons, and out of the ordinary course of common law, in right of his regal dignity ... it can only be applied to those rights and capacities which the King enjoys alone, in contradiction to others, and not to those which he enjoys in common with any of his subjects.

[6] The royal prerogative was a way to exercise his power without the consent of others but its limits were unclear and an attempt to legally define its scope was first made in 1387 by Richard II.

[7][8] This "turbulence" began to recede over the course of the 16th century and the monarch became truly independent when Henry VIII and his successors became head of a Protestant Church of England, and therefore answerable neither to the clergy nor the Pope.

Although the monarch was "the predominant partner in the English constitution", the courts recognised the growing importance of Parliament by stopping short of declaring him all-powerful.

One suggestion is they recognised stable government required legal advice and consent, while "all the leading lawyers, statesmen and publicists of the Tudor period" agreed everyone was subject to the law, including the king.

[12] James I of England challenged this consensus in the 1607 Case of Prohibitions, arguing the king had a divine right to sit as a judge and interpret the common law as he saw fit.

Until he had gained sufficient knowledge of the law, he had no right to interpret it which Coke also pointed out "requires long study and experience, before that a man can attain to the cognisance of it".

[14] The power to dissolve parliament is "perhaps the most important residual prerogative exercised personally by the sovereign, and represents the greatest potential for controversy.

In more modern times, the monarch left it to the politicians involved to choose a successor through private consultations (Winston Churchill in May 1940, Harold Macmillan in January 1957, Alec Douglas-Home in October 1963).

Nowadays, the monarch has no discretion, as the governing party will elect a new leader who will near-automatically be appointed as he or she commands the support of the majority of the Commons (most recently Theresa May in 2016, Boris Johnson in 2019, Liz Truss and Rishi Sunak in 2022).

[24][25] Granting nolle prosequi is done by the Attorney General of England and Wales (or the equivalent in Scotland or Northern Ireland) in the name of the Crown, to stop legal proceedings against an individual.

It is the monarch who recognises foreign states (although several statutes regulate the immunities enjoyed by their heads and diplomatic representatives), issues declarations of war and peace, and forms international treaties.

Under the Crown Proceedings Act 1947, the monarch is the sole authority for the armed forces, and as such their organisation, disposition and control cannot be questioned by the courts.

[40] This exercise of prerogative power gives the Crown authority to recruit members of the armed forces, appoint commissioned officers, and establish agreements with foreign governments to station troops in their territory.

[41] The prerogative empowers the monarch to appoint bishops and archbishops in the Church of England,[42] and to regulate the printing and licensing of the Authorised (King James) Version of the Bible.

[citation needed] R v Secretary of State for the Home Department, ex parte Northumbria Police Authority, recognised that the prerogative also includes the power to "take all reasonable steps to preserve the Queen's peace", and in Burmah Oil Co. v Lord Advocate, the House of Lords took the view that it extended to "doing all those things in an emergency which are necessary for the conduct of [the Second World War].

[56] Another extension came with R v Secretary of State for the Home Department, ex parte Fire Brigades Union,[57] where the Court of Appeal held that even if a statute had not yet come into force, the prerogative could not be used to "conflict with Parliament's wishes" (in that case using its discretion to choose a start date to delay, perhaps indefinitely, the introduction of a statutory compensation scheme).

[58] Whilst the royal prerogative is deployed by the UK government when making (and unmaking) treaties, the Supreme Court held in R (Miller) v Secretary of State for Exiting the European Union that the government could not use the prerogative to serve notice of termination of the UK's membership of the EU (under Article 50 of the Treaty on European Union).

On the assumption – later proven false[note 1] – that triggering Article 50 would inevitably result in Brexit, using the prerogative in this way would therefore frustrate the intention of Parliament to confer those rights.

This reasoning was maintained in the subsequent Supreme Court hearing, although that judgement devoted more attention to the fact that Parliament had voted the UK into what was then the EEC by statute in 1972, which under the principle of De Keyser's Hotel (1920) superseded the normal prerogative power to enter into treaties.