The Role of Parliament in the UK Constitution: Authorising the Use of Military Force Contents


The decision to engage in military action is one of the most serious a country can take. The legal authority to use military force is derived from the non-statutory, executive authority of the royal prerogative, a power still held by the Sovereign. However, over the centuries as political attitudes and constitutional arrangements in the UK have developed, the powers under the royal prerogative have been exercised by others acting on the Sovereign’s behalf. It is now a long-standing convention that the Prime Minister, together with the Cabinet, exercises the power to deploy military force on behalf of the Sovereign.

The legitimacy of the Government’s use of the prerogative power to order military action is derived from the elected House of Commons and the Government’s military decisions will continue to have this legitimacy as long as it maintains the confidence of the House. Against this background, it is vital that Members of Parliament understand their role in conferring legitimacy on the Government’s decisions. It is properly for the Government to develop policy and make decisions in relation to military action and foreign affairs; and it is the role of the House of Commons to scrutinise, analyse and ultimately approve or reject the Government’s policy and decisions. Nothing should compromise the ability of governments to use military force when our national or global security is threatened, but a clearer role for the House of Commons is necessary in order to underline the legitimacy of the use of military force, and to give the public confidence that the Government is being held to account.

This relationship between the Government and Parliament has been established since the Second World War in the convention, followed by successive governments, that the Government will consult the House of Commons to ensure that the will of the House is supportive of the Government’s policy on armed conflict. This convention was further developed in 2003 when, for the first time, the Government sought prior approval from the House of Commons for the Iraq war. This vote signified a shift in the expectations of Parliament and the British people that, where possible, the consultation of the House of Commons should include an explicit vote in advance of major military action. The emergence of a post-2003 convention was then confirmed by the votes held on military action in Libya in 2001 and Syria in 2013.

We found a consensus in the inquiry concerning the post-2003 convention; that the Government is expected to seek prior authorisation from the House of Commons before taking military action, subject to certain exceptions where public debate before military action would not be possible or appropriate. The exceptions to the convention are important as the Government requires discretion in relation to the most effective means of protecting the UK’s security and interests. There is, however, a legitimate concern that the Government remains the sole arbiter of what military action requires prior approval under the post-2003 convention, something which could create uncertainty. To address this concern, we recommend that, where the Government takes action under an exception to the convention, it should subsequently make a statement to the House and where necessary seek retrospective approval. In addition, we consider that the Government should provide a report to the Defence Committee setting out its reasons for acting without prior consultation.

We found that the reference in the Cabinet Manual to conventions on ordering military action lacked clarity and have recommended that the Manual be updated to set out an accurate account of the conventions. We also conclude that, while the involvement of Parliament at the earliest opportunity is vital, any statutory formalisation of this expectation would create new risks, given the difficulty of legislating for all possible contingencies. We were, however, not convinced by the Government’s arguments against developing clearer political expectations through a resolution of the House of Commons. We therefore recommend that the House of Commons considers and approves a resolution setting out the principle of the convention so that the Government, Members of Parliament and, importantly, the public are clear on what the expectations are when it comes to decisions on using military force.

It is the function and responsibility of those in Government to make policy and take decisions to protect the security of the UK. Scrutiny of Government policy and actions is a fundamental function and responsibility of Parliament, which falls particularly on Members of the House of Commons as elected representatives. Scrutiny performs a vital constitutional role as it ensures that the actions taken by the Government, on the authority of the House of Commons, are checked and where necessary adapted or halted. It is clear to us that strong scrutiny leads to better decision-making and this applies as much to policy and decisions on military action as it does to other areas of government policy. Scrutiny by the House of Commons should provide the public confidence that the Government is being held to account and that any military action taken is legitimate. The post-2003 convention has increased the opportunity for advance scrutiny of government policy in relation to major military action. However, we also conclude that other mechanisms to scrutinise Government policy and decisions are needed.

In order to carry out good scrutiny, Members of Parliament need to have sufficient knowledge and understanding of defence and foreign affairs issues. They also require access to the information necessary to carry out effective scrutiny. One of the most serious concerns raised with us during the inquiry was the widespread lack of knowledge and education of many Members of Parliament in these areas. It is the responsibility of every Member of Parliament to keep themself educated so that they are prepared to engage effectively with these most serious of issues when the nation needs them to do so. It is also vital that the Government provide the House with the necessary information to enable effective policy scrutiny. Given the sensitive nature of some of this information, there is a duty on both the Government and the House of Commons to adapt and find ways to communicate sensitive information securely.

The need to develop new mechanisms for communication is all the more important because of the changing nature of conflict, which requires rapid reaction as new challenges emerge. In areas such as cyber- and hybrid-warfare, there must be flexibility around both the Government’s decision-making process and the House of Commons’ scrutiny mechanisms. The House of Commons should consider how it best manages these competing demands. We are persuaded, for example, that the principle of how special forces and drones are utilised should be considered by the House.

In order to adapt to these challenges, we have recommended that the role of committees of the House of Commons be expanded. Giving committees greater and, in some instances, full access to information would strengthen both the scrutiny and development of policy in relation to foreign affairs and defence. We have called on the Government to propose appropriate arrangements for committees to be given access to the information which has informed the Government’s decisions about foreign affairs, military action and intelligence.

Published: 6 August 2019