The Crown, royal prerogative, and constitutional conventions

Problem scenario

In early 2025, the Conservative Government has negotiated a new international treaty with the USA. The government, concerned at the growing costs of replacing Trident, the UK’s existing nuclear deterrent, has agreed with the USA to use its nuclear technology. As part of this agreement, the UK has agreed that the USA can store nuclear missiles at US military bases located on UK territory. Prior to this agreement, the USA last stored missiles in the UK in 2006, when the last missiles were withdrawn.

Since its announcement, the treaty has provoked enormous controversy, as some believe that it reduces the UK’s standing in the world to that of a mere colony of the USA, and others are outraged by the principle of replacing the UK’s own nuclear deterrent and believe that existing nuclear missiles should be destroyed rather than replaced. Others believe that the agreement ensures the UK’s security for the foreseeable future. This debate over the treaty has come to dominate politics throughout most of 2025. Protests against the treaty have been led by several campaign groups who are now urging the Queen to intervene. They are asking Her Majesty to speak out against the treaty and prevent the government from ratifying it.

As required by the Constitutional Reform and Governance Act 2010, the government laid the treaty before Parliament. Immediately, the Opposition tabled a motion in the House of Commons, stating that the treaty should not be ratified. Many Conservative MPs have concerns over the treaty. The Prime Minister has let it be known that if the government loses the motion, they will seek to hold a general election. The House of Commons debated the motion the following day, with the government losing the vote by 310 votes to 305.

Analysing the scenario

Imagine that you were presented with this problem scenario and asked to consider how the royal prerogative operates in relation to these events.

The scenario raises several issues about individual prerogative powers. In particular, the central issue is the prerogative power to enter into and ratify international treaties. Other issues include the ability of The Queen to actively get involved in politics, and the role she plays when appointing a Prime Minister after a general election. As can be seen in the discussion of this scenario throughout Chapter 6, the exercise of the prerogative can be controlled by statute or constitutional convention.

The agreement with the United States, is an example of the prerogative power to enter into and ratify international treaties. This is an important power and is exercised by ministers. This is also an example of how the exercise of the prerogative can be made subject to requirements imposed statute, because the government is unable to ratify the agreement with the United States until the procedure outlined in the Constitutional Reform and Governance Act 2010 has been complied with. The Prime Minister may choose to proceed with a second vote as allowed by the Act, but this is a political consideration, and is an example of how the bare legal rules are often overlaid with a variety of political considerations. This blend of law and politics is a key feature of public law and means that gaining an understanding of the legal rules alone can be far from understanding the whole picture. Had the treaty been less controversial, the government may well have insisted on holding a second vote.

The difference between the legal rules and political reality is also shown by the demands from campaigners that The Queen should personally intervene and prevent the ratification of the treaty. This clearly would be going against the ‘cardinal convention’, the convention that the monarch always acts on the advice of the government.

A common theme between the controls over the power to enter into treaties, and limitations on the political activities of the monarch democracy and accountability. The government can be required to account to Parliament for how they have negotiated an international treaty. If Parliament disagrees with a treaty, they can require the government to at least reconsider, or explain further why they wish to ratify the treaty. Similarly, the refusal of the monarch to intervene, ensures that it is the elected politicians who are accountable for the decisions that the government makes. Not only are politicians accountable to Parliament, but they are also accountable to the electorate at a general election. Should the monarch become actively involved in political issues, they would interfere with this process and weaken the accountability of the government to both Parliament and the electorate.

The position of Parliament over the Crown was shown in R (Miller) v Secretary of State for Exiting the European Union, which is discussed at length in Section 6.4.3. Because sovereignty rests with Parliament and not the Crown, the view of the Supreme Court was that Parliament was required to pass legislation to invoke Article 50 as Parliament in enacting the European Communities Act 1972 had removed this power from the royal prerogative. Ultimately, it is Parliament and not the royal prerogative that can change the law. However, the decision of Miller is unlikely to be applied to other treaties because of the unique nature of the EU treaties.

In the scenario, the vote of the House of Commons against the treaty with the United States has caused an early general election in early 2025. Here, we can see that the prerogative power to appoint a new Prime Minister is heavily constrained by convention, leaving extremely little scope for the Monarch to make any personal choice. The constitutional conventions operate to ensure that the democratic will of the people as expressed in the general election is fulfilled. In a hung Parliament, who the electorate wish to form the government can be far from clear, and the result of the election raised a series of different possibilities, although it must be stressed that the task of determining who should form the next government falls to politicians and not the monarch.

The political considerations have changed with the enactment of the Dissolution and Calling of Parliament Act 2022. This abolished the Fixed-term Parliaments Act 2011, which ‘abolished’ the prerogative power to dissolve Parliament, and so trigger a general election. The 2011 Act meant that MPs could vote against the government, but if the Prime Minister tabled a motion for an early general election, MPs could vote against that. However, the 2022 Act ‘revives’ the prerogative power of dissolution. This means that a Prime Minister can once again make the threat that the Prime Minister has done in this scenario. They now have the option to seek a dissolution of Parliament, carrying out their threat given that MPs have voted against the treaty.

The final issue is that a Prime Minister “requests” that the Monarch dissolves Parliament. It is not an absolute right, and in certain, extremely limited circumstances, the monarch can refuse such a request. However, in these circumstances, in which a very significant matter of policy has caused such significant political controversy, the Monarch would grant the dissolution, leading to a general election. The policy of each party on the treaty with the United States would presumably figure extremely large in the election campaign. This means that via the democratic process of a general election, it would be the electorate who would have the final say over whether the UK ratified the treaty with the United States.

As can be seen from this discussion, the issues that this scenario raises show how fundamental a part the royal prerogative still plays in the constitution.