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

3War power conventions

Historic role of conventions

34.Convention plays an integral role in the UK’s constitutional arrangements for how military force is authorised, as in other parts of our constitution. The convention that the Prime Minister, together with Cabinet, takes decisions in relation to the deployment of the UK’s Armed Forces is so well established that many may no longer even think of it as a convention.46

35.Following the 2003 parliamentary vote to authorise military action in Iraq, many argued for a new convention to be established, that the House of Commons be asked to give prior approval for the UK’s engagement in major military action. This “post-2003 convention”, however, can be analysed against the modern history of decisions on military action.

The emergence of a stronger parliamentary convention

36.While the vote on military action in Iraq in 2003 is viewed as a pivotal point in how the UK decides to engage in military action, it is important to consider the 2003 vote in the wider context of how the UK has engaged in military action since the Second World War. Throughout this period, governments have consulted Parliament on foreign affairs and military action seeking both “in principle” and “retrospective” approval for military action both on motions for the adjournment and on substantive motions:

37.In 2002, when the possibility of military action in Iraq became apparent, a number of Members raised the issue of whether the House would be given a vote ahead of military action.56 The Government subsequently held two votes on substantive motions approving the Government policy as events developed and ultimately put down the substantive motion on 18 March 2003 seeking the approval of the House of Commons for military action.57

38.Since the Second World War, it has been the practice of successive governments to consult the House of Commons to ensure that the will of the House is supportive of the Government’s policy on armed conflict. On a number of occasions, the Government has also sought and been granted retrospective support for military action. The decision to seek prior approval from the House of Commons for the Iraq War in 2003 was the first example in modern times of a government seeking approval in advance of specified military action. While circumstances particular to the question of the 2003 Iraq War were a factor, the decision to seek prior approval from the House of Commons represented a further development of the convention that the government of the day should consult the democratically elected House of Commons in its use of the royal prerogative before the Prime Minister gives orders to use military force.

39.The Cabinet Manual, published in 2011, serves as the Government’s “guide to laws, conventions and rules on the operation of government”, although the Leader of the House told us that it is “a record of those rules and practices and not the source of any rule”.58 In his preface to the Cabinet Manual, Sir Gus O’Donnell, Cabinet Secretary at the time of publication, states that it is intended to act as “an essential guide to our system of Government”.59 It includes three paragraphs of guidance on the practice of the Government in relation to decisions on taking military action. The first of these paragraphs states:

Since the Second World War, the Government has notified the House of Commons of significant military action, either before or after the event, by means of a statement and has in some cases followed this with a debate on a motion for the adjournment of the House.60

40.The footnote to this paragraph of the Cabinet Manual gives three examples of instances when motions to adjourn were used to inform the House: “Afghanistan (4 and 8 October 2001); Kosovo (24 March 1999); and the Gulf War (17 and 21 January 1991)”.61 However, while debates in relation to Afghanistan and Kosovo were on a motion to adjourn, the 1991 Iraq vote was on a substantive motion.62

41.It is important that the Cabinet Manual recognises that a convention has been in place since the Second World War that the Government will consult the House of Commons to ensure that the Government’s policy on armed conflict reflects the will of the House of Commons. The Cabinet Manual should be updated to this effect. As currently drafted, the Cabinet Manual may give the erroneous impression that seeking the view of the House of Commons has been and could be treated as a formality. We further recommend that the Cabinet Manual should be updated to make clear that there are precedents for debates of this nature to take place on a substantive motion and not just on motions for the adjournment.

The 2003 precedent

42.The 2003 vote on the Iraq War stimulated considerable debate on how the decision to participate in the invasion and occupation of Iraq was taken within Government; and in relation to the specific information made available to Parliament prior to the Commons vote to approve the Government’s proposed military action. These issues have been extensively examined in Sir John Chilcot’s Report of the Iraq Inquiry (the “Chilcot Report”).63 The 2003 vote also raised more fundamental constitutional questions about how decisions to use military force are taken in the UK. Committees of both Houses of Parliament have considered this issue in detail, with both the Public Administration Select Committee in 2004 and the House of Lords Constitution Committee in 2006 concluding that approval of the House of Commons should be sought before major military action is taken.64 In 2007, following an Opposition Day debate, the House of Commons resolved, and the Government accepted, that a precedent was:

“ … set by the Government in 2002 and 2003 in seeking and obtaining the approval of the House for its decisions in respect of military action against Iraq [and] is of the view that it is inconceivable that any Government would in practice depart from this precedent.”65

43.There was almost unanimous agreement in evidence to this inquiry that the 2003 parliamentary vote to authorise the Iraq War set a precedent which, when combined with the actions of subsequent governments, has established a convention that Parliament should be consulted in advance over military action.66 Against the background of the 20th Century convention, outlined above, that Parliament should be consulted over military action (although not necessarily in advance), this can be seen as an incremental development rather than a great leap forward.

44.Sebastian Payne told us that the Iraq War has given rise to an expectation in the House of Commons that the House will be given a vote in advance of military action, but in circumstances such as emergency action a vote may need to be retrospective.67 Dr Strong went further, saying that, in addition to a general acceptance of the convention among Members of Parliament, there is now a majority of the public that also expects Parliament to have a vote on military action, and that it would raise questions of legitimacy if a vote were not held.68 He explained that while the House of Commons does not have legal authority to veto military action, the post-Iraq conflict convention has meant it has exercised a “de facto veto”.69 Lord Hague told the Committee that it would be “bizarre” if Parliament did not take part in the debate to take a premeditated decision to go to war. Both he and Jack Straw said that in a democracy the most serious decisions taken by the Government should be subject not only to scrutiny but, where possible, advance endorsement.70

45.Former leaders of the three UK Armed Forces (General Sir Richard Barrons, Admiral Lord West, and Air Chief Marshal Sir Glenn Torpy), raised concerns that military advantages could be lost through a prior public debate and vote on military action. They acknowledged, however, that a convention had been established in relation to the precedent set by the vote on the Iraq conflict in 2003. General Barrons told us that, if there was a planned military campaign with the scale of advance notice as for the 2003 Iraq campaign, “it would be remarkable if Parliament did not have a voice in this as a way of gauging public sentiment”.71 Similarly, Admiral Lord West stated that “[i]f you are trying to generate huge force for an old-fashioned type war then obviously, as the General says, you need to have these sorts of debates because doing that takes time”.72

46.Addressing the timeline for the development of the convention, Air Chief Marshal Torpy noted that, although the 2003 convention requiring advance approval from the House of Commons was set out in the Cabinet Manual, the 2003 precedent was only followed for the first time in the 2013 debate and vote on whether military action should be taken in Syria.73 The Government lost that vote and the planned military action never took place. On this basis, Air Chief Marshal Torpy said that, “While there appears to have been a convention since 2003, the degree to which that has been recognised or implemented has only since 2013 been enacted.”74 In other words, a precedent only becomes a precedent - or in this case, a convention - if it is followed in practice.

47.A similar assessment of the development of the convention was given by Professor Phillipson, who explained that a convention is not established at the first occurrence of a procedure, but later on, when it is identified as, and followed as, a precedent. He identified the key moment when the 2003 vote was treated as a precedent as the decision in 2011 under the Coalition Government to give the House a substantive vote on the 2011 Libya campaign, albeit after action had actually commenced because there was no time for prior approval (which is probably why Air Chief Marshal Torpy did not reference this debate in his argument on the same point). According to Professor Phillipson’s argument, the convention then held when the House of Commons declined to approve action in Syria in 2013; and when the House agreed to air strikes in Syria following a vote in2015. Lord Hague confirmed that the Coalition Government held the view in 2011 that it should consult the House in advance of military action and, by 2013, considered this an established convention.75

48.The Chancellor of the Duchy of Lancaster also considered that the 2003 vote set a precedent that has led to the development of a new convention. He told us, “I do think that Iraq in 2003 was something of a turning point here. It has been largely on the back of that experience that we have seen the modern convention develop”.76

49.There is a general consensus that the 2003 vote in the House of Commons to give approval for military engagement in Iraq in advance of the commencement of conflict set a precedent. This is a development of the pre-existing convention that the House of Commons should be consulted, to include an explicit vote in advance of major military action

50.The vote in 2003 did not itself establish the convention. Rather, it signified a shift in the expectation of Parliament and the British people that was demonstrated through recommendations by committees in both Houses of Parliament. This was also confirmed in the House of Commons in 2007 by approval of an Opposition Day resolution. The Government then recognised that a convention was emerging, and this convention was confirmed by the votes on military action in Libya in 2011 and Syria in 2013. It has for some time been unthinkable that major planned military action would not be openly discussed in Parliament. There is now an expectation that the Government would seek prior approval for such an action, where practicable to do so.

The post-2003 convention and its exceptions

The core post-2003 convention

51.In the course of our inquiry, we have found broad agreement about the nature of the post-2003 convention.77 As the Cabinet Manual explains, in respect of the two most recent examples of significant military action in Iraq and Libya, “Parliament has been given the opportunity for a substantive debate”.78 The Manual goes on to state that:

In 2011, the Government acknowledged a convention had developed in Parliament that before troops were committed the House of Commons should have an opportunity to debate the matter and said that it proposed to observe that convention except when there was an emergency and such action would not be appropriate.79

The Government restated this formulation in its written evidence to this inquiry, emphasising that the convention related to conflict decisions rather than routine deployments.80

52.Dr Strong described the convention as being that:

“MPs should have the right to veto major overseas military combat operations, unless the emergency nature of the situation or the clandestine nature of the operation proposed precludes open prior discussion in the House of Commons.81

53.Lord Hague singled out Dr Strong’s evidence as providing a good definition of the convention, but added that there are still “many areas of uncertainty”.82 Jack Straw also agreed with this formulation of the convention and indicated that the core of the convention was clearly understood when he said:83

There is now the clearest possible appreciation by Ministers of every party that if there is a major decision to be made about military action, it has to go to the House of Commons for approval and it has to be on a substantive motion.84

54.Jack Straw’s assessment was reflected in the evidence from the Chancellor of the Duchy of Lancaster and the Minister for the Armed Forces, who were both clear that troops would not be deployed without prior consultation with Parliament unless certain exceptions applied.85 The Chancellor of the Duchy of Lancaster told us:

The convention makes it clear now that Government have a duty to seek prior authorisation from Parliament, unless there are good reasons not to do so and, if those good reasons do exist, nevertheless to come to Parliament at the earliest opportunity and be held to account for the decisions that have been taken and to explain those decisions.86

55.We have found a general consensus in the evidence to this inquiry that the Government is expected to seek prior authorisation from the House of Commons before taking military action, subject to certain exceptions, such as the need to respond quickly or if it would otherwise preclude open, prior debate in the House of Commons. Furthermore, where exceptional action is taken without prior approval, the Government is expected to come to Parliament at the earliest opportunity to explain and be held to account for its decisions.

Exceptions to the duty to consult the House of Commons in advance

56.While we found consensus in the evidence around the core convention, there was also consensus that a considerable degree of uncertainty remains in relation to the scope of its exceptions.

57.The Government told us that it views the exceptions to the convention as “important to ensure that this and future governments can use their judgement about how best to protect the security and interests of the UK”.87 Both the Minister for the Armed Forces and the Government’s written submission expanded on the exceptions set out in the Cabinet Manual and elucidated what the Government now views as the four bases for taking military action without prior consultation in Parliament:

First, where it could compromise the effectiveness of our operations and the safety of British service men and women. Second, to protect our sources of secret intelligence. Third, so as not to undermine the effectiveness or security of operational partners. Fourth, where the legal basis for action has previously been agreed by Parliament.88

58.Professor Phillipson said that the scope of the exceptions to the convention was uncertain, describing them as “vague”.89 Sebastian Payne was clear that there needed to be some exceptions, but worried that a lack of clarity about their scope could render the convention of consulting Parliament pointless.90 When asked about this concern, both Jack Straw and Lord Hague agreed there was a need for greater clarity, however they were equally clear in rejecting the idea that the convention might be pointless. They considered that the convention, even with its grey areas, would clearly apply if situations similar to the Second World War, the Korean War, Falkland Islands, Iraq or Libya arose again, and in such circumstances the convention would require the Government to seek the support of the House of Commons for proposed military action.91

59.Jack Straw told us that the uncertainty around the exceptions should be addressed by clarifying the circumstances in which the House of Commons should be invited to debate government decisions to be involved in military action. However, he was clear that, as there is widespread agreement that the Commons should not sit in the place of the Government:

some decisions have to be effected and implemented without coming to the Commons, there is always going to be a grey area where it will be a matter of judgment for the senior Ministers of the day as to whether the Commons is involved.92

60.From the military perspective there was a clear need for exceptions to the convention to be understood. Admiral Lord West thought there were many circumstances in which parliamentary debate before military action might be a “real problem” and that he was “not at all sure it is the best thing”.93 Rather than debating military action in advance, he thought it was important for parliament to carry out post-hoc scrutiny of the basis for Government decisions.94 Air Chief Marshal Sir Glenn Torpy raised the concern that previous uncertainty around consulting Parliament in advance of military action in Iraq had led to a protracted decision-making process. He cautioned that, if this occurred in future, it could “undermine the ability to generate the forces and then deploy them”.95 General Sir Richard Barrons said that evolving modes of conflict meant that surprise and discretion were increasingly important and there may in future be a number of operations that the House of Commons would need to debate after the action was launched.96

61.When asked what he thought the exceptions to the convention should be, the Chancellor of the Duchy of Lancaster said that he thought they were: where there is a need for “operational flexibility” so that commanders do not have to “await a steer from Westminster” and can take the decisions in order to “deliver the mission that Ministers on behalf of the Crown have given them”;97 where there is a need for secrecy in advance of the operation so it is not compromised; where ministers have to act in an emergency; and he also suggested there may be a need for exceptions in areas were conflict is unclear, such as hybrid conflict and warfare.98

62.Lord Hague said that the areas of uncertainty were, in particular, highlighted by decisions over military action in Syria in 2013 and 2018. In relation to the 2013 action, when he was Foreign Secretary, Lord Hague said that:

I think that we probably did in several ways judge it incorrectly, but since all we had ever had in mind in that situation was a rapid, limited, one-off operation, not boots on the ground and becoming involved in a wider conflict, in retrospect, as indeed we saw last year when the Government took military action on Syria, it would have been better to make that decision.99

The difficulty with that vote, he said, was that the Government had come to the House advocating for a much smaller military action than had previously been taken. But the Government had not been able to explain, for “good operational reasons just how limited it was going to be, and then a misunderstanding can arise in Parliament”.100 This assessment was shared by General Barrons, Commander of the Joint Forces Command during this period, who said that the “discussion in officialdom that had gone to a point of certainty that this was the right thing to do” but that there was a “failure of political mobilisation”.101

63.The 2018 Syria military action, taken without prior consultation with Parliament, was used by several people as evidence for how the Government can limit the scope of the convention. Dr Tara McCormack, University of Leicester, observed that Prime Minister Theresa May’s statement to the House of Commons following the 2018 Syria airstrikes both confirmed the Government’s acceptance of the convention and, at the same time, potentially limited its scope by saying that the air strikes she ordered did not fall within the remit of the convention.102 Dr McCormack noted that the airstrike action taken in 2018 was essentially the same as in 2013 and 2015 when Prime Minister David Cameron asked the Commons for authorisation.103 Both Professor Phillipson and Professor Lagasse also told us that the Prime Minister’s speech indicated a broader exception than had previously been thought. They both considered that it demonstrated the Government’s ability to determine and alter the scope of the convention and that this increased uncertainty.104

64.There is consensus around the need for exceptions to the convention that, where possible, the Government will seek parliamentary approval for planned military action. The Government should be able to exercise its judgement about how best to protect the security and interests of the UK. We note that the Government has set out four broad bases under which it might not seek prior authorisation. These are, where it could compromise the effectiveness of UK operations and the safety of British service men and women; to protect the UK’s sources of secret intelligence; so as not to undermine the effectiveness or security of operational partners; and where the legal basis for action has previously been agreed by Parliament.

65.However, there is also a legitimate concern that the Government will remain the sole arbiter of what constitutes military action such as would require parliamentary approval under the post-2003 convention; what the exceptions to the convention are; and whether the planned military action falls under one of these exceptions. This is of particular importance in respect of clandestine operations and other areas of sub-conflict confrontation which are becoming much more frequent, and this includes instances when Parliament may not even be notified of actions that could quickly escalate into full conflict.

66.We attach the highest importance to the concerns expressed by former leaders of the Armed Forces about the possibility of parliamentary consultation on proposed military action leading to a protracted decision-making process and the potentially negative implications this could have for military preparations. It is important that Parliament, and in particular the House of Commons, is cognisant of the need for nimble decision-making and the Government would be right to reflect this in the way the convention is applied.

67.In line with our earlier conclusion, it is clear that the reference to the post-2003 convention in the Cabinet Manual lacks clarity. This may have been the cause of some unnecessary uncertainty around the convention. The Cabinet Manual is not the source of this or any other rule, but it is viewed by many as an essential guide. The Cabinet Manual should be an accurate record and give an accurate and up-to-date account of how the convention will be applied.

68.The Cabinet Manual should be reviewed and updated to set out an accurate account of how the conventions around the use of the royal prerogative power in relation to military action will be applied, together with a clearer exposition of the exceptions to those conventions. References should identify sources of authority and precedent.


46 Oral evidence taken on 23 October 2018, Status of Resolution of the House of Commons, HC 1587, Q92 [Professor Blackburn]

47 A debate was held on 6 and 7 May 1941 on a motion of confidence, to approve the Government’s policy to send help to Greece; and to declare the confidence of the House that “war will be pursued by the Government with the upmost vigour”. The motion was agreed to on division, by 447 to 3. HC Deb, 6 May 1941, col 727–826, [Commons Chamber], HC Deb, 7 May 1941, col 867–950, [Commons Chamber]

48 HC Deb, 5 July 1950, col 485, [Commons Chamber]; That this House fully supports the action taken by His Majesty’s Government in conformity with their obligations under the United Nations Charter, in helping to resist the unprovoked aggression against the Republic of Korea; In the run up to military action the Leader of the Opposition, Winston Churchill, was clear to express the Opposition’s confidence in the Government to meet their international obligations. In the debate on the substantive motion he said: We consider that the Government were right to place a Motion on the Order Paper asking for approval in general terms of the course which they have adopted since the invasion of South Korea began. There are grave dangers, as we learned in the war, that false impressions may be created abroad by a Debate prominently occupied by a handful of dissentients. It is better to have a Division so that everyone can know how the House of Commons stands and in what proportion. Should such a Division occur, we on this side will vote with the Government. HC Deb, 5 July 1950, col 495, [Commons Chamber]

49 HC Deb, 13 September 1956, col 163, [Commons Chamber]; Parliamentary approval for military action, House of Commons Library Briefing paper CBP7166, 8 May 2018

50 HC Deb, 01 November 1956, col 1631–1744, [Commons Chamber]

51 HC Deb, 03 April 1982, col 633, [Commons Chamber]

53 HC Deb, 17 January 1991, col 979–96, [Commons Chamber]; HC Deb, 21 January 1991, col 23–110, [Commons Chamber];

54 Concern was expressed for example by Tony Benn who said: “It is a matter of great concern, not least because of our anxiety in respect of the troops and their families. We have had three debates on the adjournment without substance. Today, we are having a debate without choice…The point I am seeking to make is not only that different views should be expressed, but that they should be able to be tested in the Lobby, so that Parliament is seen as a place where different views can be registered”. HC Deb, 21 January 1991, col 23, [Commons Chamber]

55 HC Deb, 24 March 1999, col 483, [Commons Chamber]; Rt Hon Douglas Hogg raised the concern that action was being taken “without the authority of the House”. HC Deb, 24 March 1999, col 489, [Commons Chamber]; Others such as Rt Hon Tony Benn expressed concern over the Government’s reluctance to hold a debate on a substantive motion that would have allowed Parliament to record its view on the Government’s policy over Kosovo. HC Deb, 25 March 1999, col 619, [Commons Chamber]; Parliamentary approval for military action, House of Commons Library Briefing paper CBP7166, 8 May 2018; HC Deb, 14 September 2001, col 604–670, [Commons Chamber]; HC Deb, 8 October 2001, col 671–810, [Commons Chamber]; HC Deb, 8 October 2001, col 812–902, [Commons Chamber]; concern was for example expressed by Paul Marsden, who said: “There is growing disquiet that for the third time Parliament has been recalled yet hon. Members have been denied a vote on this war. Can you confirm to me that there will be no vote? Is it in order for hon. Members to vote on an adjournment debate if similar occasions arise, when we are denied a substantive motion by the Government?” HC Deb, 8 October 2001, col 829, [Commons Chamber]

56 For example, the Leader of the Liberal Democrats Rt Hon Charles Kennedy said: There is no specific proposal before the House today, but, if and when there is one, there must be an absolute, up-front opportunity for the House to vote on any proposal involving the possible use of British forces. In his statement today, the Prime Minister said that the House would be kept fully “in touch”. Does “in touch” mean a democratic Division in the Lobby of the House? HC Deb, 24 September 2002, col 10, [Commons Chamber]

57 HC Deb, 25 November 2002, col 47–129; HC Deb, 26 February 2003, col 265–363, [Commons Chamber]; HC Deb, 18 March 2003, col 760, [Commons Chamber]

58 Letter from the Leader of the House, 4 December 2018; Cabinet Office, The Cabinet Manual, October 2011,

59 Cabinet Office, The Cabinet Manual, October 2011, v

60 Cabinet Office, The Cabinet Manual, October 2011, 5.36

61 Cabinet office, The Cabinet Manual, October 2011, chapter 5 footnote 34

62 HC Deb, 21 January 1991, col 23–110, [Commons Chamber]; Substantive motions were also passed for example for Korean War and in relation to the Suez crisis in 1956

63 The Iraq Inquiry, July 2016, The Report of the Iraq Inquiry

64 Public Administration Select Committee, Fourth Report of Session 2003–04, Taming the Prerogative: Strengthening Ministerial Accountability to Parliament, HC 422; House of Lords Select Committee on the Constitution, fifteenth report of the session 2005–6, Waging war: Parliament’s role and responsibility, HL 236-I

65 HC Deb, 15 May 2007, col 579–582, [Commons Chamber]

66 Only the Society for Conservative Lawyers has argued that the 2003 Iraq vote should not be considered as a precedent and that, consequently, a convention around prior parliamentary approval has not been established. Society of Conservative Lawyers (UMF0017)

69 Dr James Strong (UMF0003)

73 HC Deb, 29 August 2013, col 1425–1556, [Commons Chamber]

74 Q133, Q154 [Air Chief Marshal Sir Glenn Torpy]

77 Professor Philippe Lagasse (UMF0006);Professor Gavin Phillipson (UMF0009);Dr Tara McCormack (UMF0008)Mrs Susan Rogers (UMF0010);Protection Approaches (UMF0013); All-Party Parliamentary Group on Drones (UMF0018);Reprieve (UMF0019)

78 Cabinet office, The Cabinet Manual, October 2011, 5.37

79 Cabinet office, The Cabinet Manual, October 2011, 5.38

80 Cabinet Office (UMF0022)

81 Dr James Strong (UMF0003)

87 Cabinet Office (UMF0022)

88 Cabinet Office (UMF0022)

102 Q90; HC Deb, 16 April 2018, col 39–92, [Commons Chamber]; HC Deb, 16 April 2018, col 200–209, [Commons Chamber]

103 Dr Tara McCormack (UMF0008)

104 Q55; Professor Gavin Phillipson (UMF0009); Professor Philippe Lagasse (UMF0006)




Published: 6 August 2019