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

2The royal war prerogative: an executive function

The royal prerogative

7.The Armed Forces of the United Kingdom are deployed under the royal prerogative, as has been the practice for centuries. The royal prerogative powers are the source of non-statutory executive authority exercised by or on behalf of the Monarch.4

8.The royal prerogative was originally the absolute power of the Monarch and remains part of the British political system. Rt Hon Tony Benn, for example, suggested the royal prerogative originated with the declaration of William I at his coronation in 1066, meaning that some form of prerogative power has been an accepted part of the constitutional arrangements for almost a millennium.5

9.There is no single definition of the royal prerogative and its extent and use has become more limited over the centuries.6 Professor Gavin Phillipson, University of Bristol, told the Committee that the royal prerogative powers in existence today are the residue of the absolute power of the Monarch. This description stems from the constitutional lawyer, A.V. Dicey, who described the prerogative as:

“both historically and as a matter of actual 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.”7

Originally, the war prerogative was used by the Sovereign alone, then the King or Queen in Council, then the Sovereign acting through the Prime Minster. Sebastian Payne, University of Kent, told the Committee that the person or people effectively exercising the royal prerogative power has transitioned over time with the rise of “responsible Government” and the establishment of increasingly democratic institutions.8

10.The royal prerogative is the legal basis for the Executive (Crown) to act where the authority has not been set out in or curtailed by an Act of Parliament. Professor Phillipson explained that, over time, Parliament has gradually assumed most powers of the Sovereign. Parliament has mostly done this through passing Acts of Parliament that supersede and forever remove prerogative power. For example, taxation was historically an important power assumed by Parliament; and more recently the power to dissolve Parliament was removed from the royal prerogative.9 However, there are still a few, and some very significant, powers that Parliament has not taken, such as powers in relation to war and foreign affairs, which remain prerogative powers. In these areas, therefore, the Government exercises powers derived from the Sovereign and not from the legal authority of an Act of Parliament.

How has the royal prerogative developed and how has its use changed through history?

11.The idea that the Executive has exclusive powers over war and foreign policy is long-established in descriptions of the government of the UK, but the justifications have changed over time. In the 1560s, Sir Thomas Smith’s treatise on the Government and politics of England, De Republica Anglorum, made plain that both the power and the authority to wield it rested with the Monarch:

Monarch of Englande, King or Queene, hath absolutelie in his power the authoritie of warre and peace, to defie what Prince it shall please him, and to bid him warre, and againe to reconcile himselfe and enter into league or truce with him at his pleasure or the advice onely of his privie counsell.10

12.In the eighteenth century, Sir Robert Walpole said, “our constitution has trusted entirely to the Crown, the power of making peace and war”.11 This was in line with political thought during this period. For example, leading political philosophers such as Montesquieu and Blackstone were clear that executive power in general, and power over war and foreign affairs in particular, ought to be in the hands of the Crown.12 Blackstone, however, argued that, in these duties, the King is the delegate and sovereign representative of his people rather than acting through his own divine right.13

13.In the nineteenth century, Whig theories of representative government replaced those that saw the British constitution as one of mixed and balanced Monarchy. Nevertheless, the view persisted that war and foreign policy remained in the realm of executive power. The difference was that this period also marked a shift to an understanding that while, formally, the Sovereign had powers over war and foreign policy, in practice these powers were exercised on the advice of Ministers drawn from Parliament. In 1858, Rt Hon Earl Grey described the relationship:

It is the distinguishing characteristic of Parliamentary Government, that it requires the powers belonging to the Crown to be exercised through Ministers, who are held responsible for the manner in which they are used, who are expected to be Members of the two Houses of Parliament, the proceedings of which they must be generally able to guide, and who are considered entitled to hold their office only while they possess the confidence of the Parliament, and more especially the House of Commons.14

This interpretation of the operation of the royal prerogative, and therefore the powers relating to war and foreign policy, has remained dominant since the nineteenth century.

14.While there has been a clear, orthodox understanding that the war prerogative is an exclusive executive power, Parliament, and the House of Commons in particular, has, in reality and despite the protestations of the Executive, played an active and influential role in the exercise of the prerogative from the 17th Century to the present day.

15.The most obvious, but also the most exceptional, instance of Parliament influencing the use of military force was between 1648 and 1649 during the English Civil War when the powers of government, including war and foreign policy powers, were exercised by Parliament, or by a committee appointed by Parliament. In the years following the execution of Charles I, the different parliaments continued to exert some control over foreign policy and military affairs; however, these were increasingly delegated to Committees and then to Cromwell as Lord Protector. Even then, in order to dispose of standing forces, Cromwell needed the consent of Parliament while it was sitting, and the advice of the Privy Council when Parliament was not in session.15

16.While the restoration of Charles II as King reasserted the royal prerogative, it had become generally accepted that Parliament could properly debate any topics relating to war and foreign policy. Article VI of the Bill of Rights then established that raising or keeping a standing army without the consent of Parliament is illegal, a power that continues today, providing Parliament with a reserve power to take away the Government’s ability to prosecute a war. This was also an important period as it solidified the convention that the Monarch exercises prerogative powers on the advice of ministers who were drawn from Parliament.

17.As parliamentary government became more established during the eighteenth and nineteenth centuries, there was a gradual transfer of power over both domestic and foreign affairs from the Monarch to ministers sitting in Parliament, representing a relative strengthening of Parliament’s position. However, as parliamentary government became stronger, and therefore Ministers sought to exercise more control over business in the Commons, the power of Parliament to directly influence war and foreign policy waned. The nature and functions of parliamentary debates consequently changed quite significantly, moving away from considering foreign policy with the intention of shaping it towards Government using parliamentary debate to promote its policy and persuade the House of Commons, and then increasingly the public, of its merits. In turn, the House of Commons increasingly used parliamentary debate to scrutinise the Government’s conduct in war and foreign policy.

18.Rosara Joseph in her book, The War Prerogative, writes that governments took very seriously the need to explain and respond to criticism from the House of Commons. Ministers were aware that parliamentary support bolstered their position both domestically and abroad; and would provide, either on request or on their own initiative, information to the Commons about war and foreign policy. Parliament also influenced the Government’s use of executive functions through debates. Debates on foreign policy and war in the 18th and 19th centuries were frequent and detailed, and these issues were often significant features of debates on the King’s or the Queen’s Speech.16 With the expansion of the franchise and the increasing influence of democratic thought and norms within British politics and around the world, the House of Commons was viewed, not only as representative of the people but also, increasingly, as the organ for the expression of public opinion. This has led to increasing reference to and concern for public opinion on proposed military action. For example, before the start of the First World War questions were raised in the House of Commons as to whether the Government was compelled to consider its higher duty to the interests of the people before entering into war; and it was suggested that the public view on entering the conflict was to say “no”.17

The royal war prerogative today: an executive function

19.The Government said in its written evidence:

The legal authority to commit Armed Forces to conflict abroad is provided by the Royal prerogative power exercised by Ministers on behalf of the Sovereign.18

Professor Phillipson described it is a “well-established convention” that the decision to engage in armed conflict, whether alone or as part of an international coalition, is taken by the Government on behalf of the Sovereign, under the royal prerogative.19

20.In terms of the balance of power and responsibility between the Executive and Parliament in modern times, Parliament has no legal role in authorising the use of military force because, with the exception of the limited provisions included in the Act of Settlement 1700, it has not legislated to take for itself a formal role in these decisions.20 However, the existence and funding of the Armed Forces is a power held wholly by Parliament because, in accordance with Article VI of the Bill of Rights, Parliament authorises defence expenditure annually; and every five years renews the legal basis for the Armed Forces through an Armed Forces Bill.21

21.There was a clear consensus in both the written and oral evidence to the Committee that the deployment of military force is a necessary responsibility and function of the Executive.22 In particular the importance of having the ability to act with “dispatch and discretion” and having all the tools, mechanisms and knowledge to make decisions on the deployment of military force was emphasised.23 Sebastian Payne told the Committee that for him “it is the function of Government to work out the strategy and the policy” and “for Parliament to scrutinise, to analyse and maybe in some cases even to reject proposals”.24 He was clear that Parliament was not “an appropriate body to micro-manage a military campaign” rather “that is the function of Government and it is necessary”.25 Professor Phillipson agreed with Mr Payne, saying this retains the “classic Westminster system of Government” where “the Government proposes, and Parliament scrutinises and then either gives its assent or does not give its assent”.26

22.Rt Hon Jack Straw was clear in his evidence that the power to deploy military force was a responsibility of the Executive and “there is no way [a Government] can shuffle this off”.27 He told us that every Prime Minister he was familiar with:

“recognised that the burden that ultimately fell on them alone in respect of initiating military action was a very personal burden and the largest burden on their shoulders.”28

23.The royal prerogative has for centuries been the source of legal authority to wage war and conduct foreign relations. The legal authority to order the use of military force today, is still derived from the royal prerogative and the power to deploy the UK’s Armed Forces will remain under the royal prerogative unless an Act of Parliament is passed, setting out a new legal basis for the use of that power. However, who exercises these powers in practice has changed as political attitudes and constitutional arrangements in the UK have developed. In practice, the Sovereign no longer has the legitimate authority to exercise this prerogative power, which has for some time been exercised on their behalf, by ministers drawn largely from the House of Commons. The continuance of this convention is essential to the integrity of UK’s constitutional arrangements and the legitimacy of the UK’s use of military force. This convention is now unquestioned, and as such it is unthinkable that the Sovereign could exercise her own discretion in the use of this royal prerogative.

24.The development of policy in relation to foreign affairs and defence is also an executive function and responsibility. It is for the Government to develop this policy and monitor, judge and react to new information that may affect it. It is for Parliament, and in particular the elected House of Commons, to scrutinise, analyse and approve or reject the Government’s policy.

Legitimate authority

25.While the legal basis to use military force under royal prerogative has remained essentially unchanged for almost a millennium, the person wielding that power and the way in which they use it has evolved over time, in accordance with prevailing political principles and attitudes. Sebastian Payne described this as the change in the “guiding mind” that makes the decisions. Central to this development has been the relationship between Parliament and the Executive. This relationship has been developing ever since it became the accepted practice that the Monarch’s chief ministers must be drawn from Parliament and Acts of Parliament started the process of removing aspects of the royal prerogative and replacing them with parliamentary power. Sebastian Payne identified the rise of parliamentary government as the key change in the UK, which has meant “we do not expect the Monarch to take the decision because it is a constitutional Monarchy and a parliamentary democracy”.29 As such, he continued, the justification for who takes these decisions is “intimately connected to the idea of our conception of how we should be governed; what the nature of our democracy should be”.30

26.While Ministers may have previously been a balancing force on behalf of Parliament on the absolute power of the Monarchy, the Government is now viewed as the legitimate exerciser of almost all the meaningful executive and royal prerogative powers. This legitimacy comes from commanding the confidence of the elected House of Commons. In the context of a discussion on the royal prerogative power, the Chancellor of the Duchy of Lancaster told us that:

… as a consequence of the outcome of a general election and, following a general election, a decision [is taken by] the House of Commons as to whom they should entrust with the formation of the Government. The Government of the day exist for so as long they have the confidence of the House of Commons. That is the ultimate sanction that any Parliament has over any Government.31

27.Rt Hon Lord Hague and Rt Hon Jack Straw were equally clear that the legitimate authority for the Government to use the royal prerogative comes from the consent and legitimacy of holding the confidence of the elected House of Commons.32 Lord Hague told us that he now could not imagine a major military decision such as the Iraq War being taken “without explicit parliamentary consent” and that “it would not be possible or democratically legitimate in this country to do that against the will of Parliament”.33 He told us that the question we were now facing was “what is the degree of scrutiny and accountability and control that Parliament is able to exercise over that.”34 This understanding was widely expressed in evidence to the inquiry.35

28.One of the things that became apparent during this inquiry, and our wider inquiry into The Role of Parliament in the UK Constitution, is that there can be a tendency to view the British political system as one in which there is a separation of powers between Parliament and the Government, and as such they are locked into conflict. On the contrary, as Sir Stephen Laws, former First Parliamentary Counsel, told us:

… because the UK constitution, which is based, so far as the Executive and Parliament are concerned, on the confidence principle, is not one that provides for separate functions and powers of each, but one that provides for them both to be able to exercise power and that incentivises collaboration and co-operation between the two.36

Professor Alison Young added to this that while it is often said “that the idea that the Executive and Parliament are fused is in some sense the efficient secret”, as the Government has the backing of the majority party or at least the confidence of the House, it should also be recognised “that it is the duty of Parliament to hold the Executive to account for its actions”.37 This is an important function, she suggested, to counter concerns of potential executive dominance in Parliament.

29.Writing on behalf of Policy Exchange, Sir Stephen Laws, Professor Richard Ekins, and Professor Graham Gee, said that in the British system, one should not expect Parliament and Government to be routinely locked in conflict. Rather, Parliament will routinely support the Government in which it has placed confidence. Equally, it is a misconception to confine Parliament’s constitutional purpose to being simply a legislative body. On the contrary, Policy Exchange argues, “the confidence principle means that Parliament is also the source of legitimacy for everything the Government does and so is entitled to exercise powers of scrutiny over it and to call the Government to account in ways that have nothing to do with its role in relation to legislation”.38 There is, according to Policy Exchange, not a rigid division of legislative and executive acts in the British political system, as Parliament is “much more than just a legislature”.39 Parliament can decide what role it adopts and how to perform it, and, from time to time, adapts the way it conducts itself to meet the wishes of the electorate.

30.Nevertheless, Policy Exchange expressed the view that Parliament should be cognisant of the “constraints inherent in its composition”, as there are some things that are better dealt with by Government rather than a deliberative assembly of 650 people. Policy Exchange considered that these areas, which include the royal prerogative powers to conduct foreign policy or initiate military action, should be exercised by the Government but should be subject to parliamentary scrutiny and accountability.40

31.Professor Phillipson told us that a “strong and clear role for Parliament acting as a check upon governmental decisions to use military force may be seen as particularly important in the United Kingdom” because the uncodified constitution means there are no formal checks and balances present as there would be in other countries.41 He pointed out that the royal prerogative is a “non-statutory executive authority that is defined in no authoritative constitutional text and which remains unclear in scope today”.42 Given that the courts have repeatedly declared decisions of the executive to deploy military force non-justiciable, Professor Phillipson thought that the check on the Government’s power “must be a parliamentary check”.43

32.General Sir Richard Barrons, former Commander Joint Forces Command 2013–16, and Admiral Lord West, First Sea Lord and Chief of the Naval Staff from 2002 to 2006, said that, from the Military perspective, it is the job of ministers to determine what should or should not be done, and this is not an area where the military voice should be heard. Rather, General Barrons said, Parliament should have a role in overseeing the Government’s policy perspective, especially in advance of conflict situations arising, and have a voice on what the policy should be and if necessary “call it out and push back”.44 They both thought that the duty on military leaders was “to be unequivocally clear and if necessary speak truth to power” to both Government and Parliament if they are asked to do something that they knew could not be done without failing, or with an unacceptable cost.45

33.The source of the legitimacy for the exercise of the royal prerogative to order the use of military force has changed over the years. Currently, the Prime Minister, together with the Cabinet, exercises this power on behalf of the Monarch. In a parliamentary democracy it is clear that the authority for the Government to exercise the royal prerogative is derived from having the confidence of the elected House of Commons. This fact in no way diminishes the responsibility and accountability of the Government for its policy in relation to foreign affairs and the use of military force. It is, therefore, of paramount importance that every Member of the House of Commons understands that the government of the day ultimately enters into military conflict on the basis of an authority which Members themselves have conferred through the mechanism of the confidence of the House.


4 Professor Gavin Phillipson (UMF0009)

5 “I vow before the altar of Peter the Apostle and in the presence of the clergy and the people to defend the holy churches of God and their governors, to rule over the whole people subject to me justly and with royal provenance to enact and preserve rightful laws and strictly to forbid violence and unjust judgments”. Oral evidence taken before the Public Administration Select Committee on 10 April 2003, HC 46, Q1 [Rt Hon Tony Benn]

6 Sebastian Payne,’ The Royal Prerogative’, in Maurice Sunkin & Sebastian Payne (ed) The Nature of the Crown: A Legal and Political Analysis, (Oxford 1999), pp 77–110

7 A.V. Dicey, Introduction to the Study of the Law of the Constitution, Liberty Fund (1915), 828

8 Q2, Q28

10 Thomas Smith, De Republica Anglorum:The maner of governement or policie of the Realme of Englande, Chapter 3

11 Rosara Joseph, The War Prerogative, (Oxford, 2013), p 17

12 Montesquieu, L’Espirit des lois’ 1748; Sir William Blackstone, Commentaries on the laws of England, in four Books vol1, 13th Edition

13 Sir William Blackstone, Commentaries on the laws of England, in four Books vol 1, 13th Edition, 252, 256–7

14 Henry Grey, Parliamentary Government, Considered with Reference to a Reform of Parliament... (1858)

16 Rosara Joseph, The War Prerogative, (Oxford, 2013), p 62

17 Rosara Joseph, The War Prerogative, (Oxford, 2013), p 66

18 Cabinet Office (UMF0022)

19 Professor Gavin Phillipson (UMF0009)

20 The Act of Settlement 1700 provides that if the Crown were to pass to a non-UK native, Parliament must give its consent for the use of Military force in defence of realms which are not UK dominions or territories. This was to prevent English forces being used to defend Hanoverian lands following the anticipated line of succession.

21 Every five years the legislation governing the legal basis for the Armed Forces, its system of command, discipline and justice must be renewed by an Act of Parliament and in the interim must be renewed by an annual Order in council. The current legislation is the Armed forces Act 2016, which continues the provisions of the Armed force Act 2006. No order in council can be passed to continue this Act beyond the end of 2021. A new Act must be passed by that date for the armed force to continue to exist.

22 Dr Daniel Kenealy (UMF0020); Society of Conservative Lawyers (UMF0017)

23 Professor Philippe Lagasse (UMF0006); DefenceSynergia (UMF0014)

27 Q180 [Straw]

35 Reprieve (UMF0019)

36 Oral evidence taken on 29 January 2019, Parliament and the Constitution: Mechanisms allowing Parliament to direct the Executive, HC1907, Q2

37 Oral evidence taken on 29 January 2019, Parliament and the Constitution: Mechanisms allowing Parliament to direct the Executive, HC1907, Q2

38 Policy Exchange (PAC0023), para 29

39 Policy Exchange (PAC0023), para 30

40 Policy Exchange (PAC0023), para 33, 41

41 Professor Gavin Phillipson (UMF0009)

42 Professor Gavin Phillipson (UMF0009)

43 Professor Gavin Phillipson (UMF0009)




Published: 6 August 2019