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


1.The Public Administration and Constitutional Affairs Committee launched its inquiry ‘Authorising the use of Military Force’ on 29 January 20191 as part of its wider inquiry series ‘The Role of Parliament in the UK Constitution’.2

2.The decision whether or not to take military action is one of the most serious a country can take. It is a life and death decision affecting members of the UK Armed Forces and those of our adversary, as well as civilians in the UK and abroad. The purpose of the inquiry has been to review how the UK’s constitutional arrangements for deciding whether to take military action have changed in the light of significant debate following the decision to go to war in Iraq in 2003. Since 2003, committees of both Houses of Parliament and the UK Government have examined the issue of Parliament’s role in decisions to use military force. These reports provide the background against which Parliament’s role in conflict decisions has developed (Appendix 1 provides a summary of these reports and Government papers).

3.The arrangements for taking military action involve one of the main residual prerogative powers held by the Monarch and exercised on her behalf by the Government. As such, changes to how prerogative power can legitimately be used in relation to military action have significant implications for other areas of the UK’s constitutional arrangements. This inquiry seeks to provide a thorough assessment of the current constitutional landscape and make recommendations for the future.

4.For at least two centuries, it has been expected that, when taking decisions about military force on behalf of the nation, the Government will take into account military and logistical limitations and how they relate to the effectiveness of the proposed military action, the political limitations, and the legitimacy of the action. In any military action, the Government must have the consent and support of the people it serves. If there are doubts about this consent and support, this will undermine the effectiveness of the military action. It follows that the Government does not take these decisions in a vacuum: it has always been necessary for the Government to engage with those to whom it is held accountable.

5.These considerations have been recognised and variously interpreted since Clausewitz set out his ‘remarkable trinity’ in his defining work On War.3 For our purposes, it can be best represented as a triangle:

This report sets out contemporary expectations in relation to how the Government will take decisions to engage in military action, ensuring that the action will have sustainable effect and be viewed as legitimate both by the British people and internationally, including by our adversaries.

6.For the avoidance of doubt, this inquiry has not considered the issue of the UK’s nuclear deterrent.

2 PACAC, “The Role of Parliament in the UK Constitution”, 13 September 2018

3 Carl von Clausewitz, On War, (Princeton, 1976)

Published: 6 August 2019