The Royal Prerogative in UK Constitutional Law

The Royal Prerogative comprises the residual powers and privileges of the Crown that are recognised by the common law. These are powers that historically belonged to the monarch but are now exercised predominantly by ministers on behalf of the Crown. The prerogative is a significant source of executive authority in the UK constitution, governing matters as diverse as the conduct of foreign relations, the deployment of armed forces, the appointment of ministers, and the grant of honours. Unlike statutory powers, prerogative powers are not conferred by legislation but are recognised by the common law as inherent attributes of the Crown. The scope and exercise of prerogative powers have been progressively limited by statute, judicial review, and constitutional convention.

Definition and Nature

A V Dicey defined the prerogative as “the residue of discretionary or arbitrary authority which at any given time is legally left in the hands of the Crown.” This definition captures two essential features: the prerogative is what remains after statutory intervention, and it is recognised by the courts rather than created by them. Blackstone described it as “the special pre-eminence which the King hath over and above all other persons, in right of his regal dignity.” The courts have adopted a restrictive approach to identifying prerogative powers requiring that the Crown establish the existence and scope of any claimed prerogative by reference to legal authority or historical practice. In BBC v Johns (1965), Lord Diplock stated that the courts “must be astute to see that the Crown does not claim any prerogative right which it did not have at common law.” This principle ensures that the prerogative does not expand beyond its historical limits.

Historical Scope

The historical range of prerogative powers was extensive. The Crown possessed powers relating to war and peace, the making of treaties, the command of armed forces, the governance of colonies, the appointment of ministers and judges, the summoning and dissolution of Parliament, the granting of honours and pardons, the regulation of coinage, and the administration of the civil service. Many of these powers have been curtailed or placed on a statutory footing. The Bill of Rights 1689 abolished the suspending and dispensing powers, prohibiting the Crown from suspending laws or dispensing with their execution without parliamentary consent. The Act of Settlement 1701 restricted the Crown’s power over the judiciary by establishing judicial tenure during good behaviour. The Constitutional Reform and Governance Act 2010 placed the management of the civil service on a statutory basis and codified the treaty-making process. Today, the remaining prerogative powers are primarily concentrated in areas of foreign affairs, defence, and the internal organisation of government.

The Major Prerogative Powers

The most significant prerogative powers currently exercised include the power to make and ratify treaties, now subject to the Ponsonby rule codified in the Constitutional Reform and Governance Act 2010, which requires treaties to be laid before Parliament for 21 sitting days before ratification. The power to deploy armed forces remains a prerogative power exercised by the Prime Minister and Cabinet, though a constitutional convention has developed since the Iraq War that the government should seek parliamentary approval before committing troops to armed conflict. The power to appoint the Prime Minister and ministers is exercised by the monarch under constitutional convention, appointing the person most likely to command the confidence of the House of Commons. The power to grant the Royal Assent to bills has not been refused since 1708. The power to grant pardons is exercised by the Home Secretary on behalf of the Crown under the prerogative of mercy. The power to dissolve Parliament, historically a prerogative power, is now governed by the Dissolution and Calling of Parliament Act 2022.

Judicial Review of Prerogative Powers

For centuries, the exercise of prerogative powers was considered non-justiciable, meaning the courts would not inquire into the manner of their exercise. This position changed decisively in Council of Civil Service Unions v Minister for the Civil Service (1985), the GCHQ case, in which the House of Lords held that the exercise of prerogative powers was subject to judicial review, provided the subject matter was justiciable. Lord Diplock stated that the mere fact that a power derived from the prerogative rather than statute did not immunise it from judicial review. However, the courts have recognised that certain prerogative powers remain non-justiciable, including the making of treaties, the dissolution of Parliament, the appointment of ministers, and the grant of honours. The justiciability of the prerogative power to deploy armed forces was considered in R (Campaign for Nuclear Disarmament) v Prime Minister (2002), where the court declined to determine the legality of the Iraq War, holding that such decisions were inherently political and not susceptible to judicial determination.

Codification and Reform

The trend in modern UK constitutional law has been toward the codification of prerogative powers. The Constitutional Reform and Governance Act 2010 placed the civil service on a statutory footing and codified the treaty process. The Fixed-term Parliaments Act 2011 (since repealed and replaced by the Dissolution and Calling of Parliament Act 2022) placed the dissolution power on a statutory basis. The House of Lords Act 1999 removed most hereditary peers, limiting the Crown’s power to create peerages. The Crime and Courts Act 2013 placed the appointment of the Director of Public Prosecutions on a statutory basis. Despite these reforms, substantial residual prerogative powers remain. The House of Lords Constitution Committee and the Public Administration and Constitutional Affairs Committee have repeatedly recommended further codification, arguing that prerogative powers should be placed on a statutory footing to enhance parliamentary accountability and legal certainty. Critics of codification contend that the prerogative provides necessary flexibility for the government to act decisively in matters of foreign affairs and national security, and that the existing conventions and political accountability mechanisms provide sufficient constraint.

The Continuing Debate

The royal prerogative remains a contested feature of the UK constitution. Critics argue that prerogative powers are anachronistic, conferring significant executive authority without democratic legitimacy or adequate parliamentary scrutiny. The war prerogative has attracted particular attention, with the House of Commons passing a resolution in 2024 requiring parliamentary approval for military action, though this resolution does not have the force of law. The prerogative of mercy has been subject to criticism for lack of transparency and consistency. The power of the Prime Minister to trigger the Article 50 withdrawal process under the Treaty on European Union, confirmed by the Supreme Court in R (Miller) v Secretary of State for Exiting the European Union (2017), demonstrated that the government could not use prerogative powers to override or nullify rights conferred by statute, establishing an important limit on the reach of prerogative authority. The case confirmed that where statute and prerogative conflict, statute prevails, and that prerogative powers cannot be used to circumvent Parliament. The future of the prerogative likely involves continued piecemeal codification rather than wholesale abolition, reflecting the incremental character of UK constitutional reform.