Recent events have led to renewed discussion about the convention that parliament should have a formal role in authorising military action, which Keir Starmer at one point proposed to codify in legislation. Robert Hazell argues that placing the existing convention on a statutory footing is unwise, and calls on parliament and the government to work together in creating a ‘shared vision’ of how the convention should operate.

Tony Blair’s decision to support the US invasion of Iraq in 2003 has cast a long shadow over every subsequent leader of the Labour party. Keir Starmer opposed the Iraq war, and one of ten pledges he promised as part of his 2020 leadership campaign was to introduce a Prevention of Military Intervention Act. He subsequently specified on The Andrew Marr Show: ‘I would pass legislation that said military action could be taken if first the lawful case for it was made, secondly there was a viable objective and thirdly you got the consent of the Commons’.

Starmer was reminded of this pledge when he was interviewed about the UK airstrikes against the Houthi rebels in Yemen. He told Laura Kuenssberg on 14 January that his proposal for military action to require the support of the Commons only meant sustained military action involving troops on the ground, rather than targeted airstrikes like those in the Red Sea:

If we are going to deploy our troops on the ground, then parliament should be informed: there should be a debate, the case should be made, and there should be a vote… What I wanted to do was to codify the convention: the Cabinet Manual has a convention… it could be in a law or it could be by some other means.

The Cabinet Manual records the convention in these terms at paragraph 5.38:

In 2011, the government acknowledged that a convention had developed in Parliament that before troops were committed the House of Commons should have an opportunity to debate.

There were many twists and turns in the genesis of the convention, and its subsequent evolution, recorded in more detail in the 2022 Constitution Unit report Reforming the Prerogative. In brief, the convention was first articulated by Tony Blair in 2003 in the parliamentary debate authorising the invasion of Iraq. Gordon Brown as Prime Minister subsequently tried to codify it in a parliamentary resolution as part of his wider initiative to codify all the prerogative powers, but ran out of time. After acknowledging the convention in the 2011 version of the Cabinet Manual, David Cameron was forced to drop military action in Syria against President Bashar al-Assad’s use of chemical weapons when he lost a parliamentary vote in 2013. Although the government won subsequent votes in 2014, for airstrikes against ISIS in Iraq, and in 2015 for airstrikes in Syria, Theresa May must have been mindful of Cameron’s defeat when, in 2018, she authorised airstrikes in Syria without seeking prior parliamentary approval. Ever since then the existence and scope of the convention has been in doubt: in 2019 the Commons Public Administration and Constitutional Affairs Committee (PACAC) described the convention as ‘seriously unstable’, and recommended that a resolution be put to the Commons to update codification of the convention.

So what are the choices facing Keir Starmer, in his wish to codify the convention, in a law or by some other means? The first option, codification in law, need not detain him long.  Gordon Brown came to recognise that specifying in statute the circumstances which would require a parliamentary debate would be too inflexible; and create an enhanced risk of court challenges. Parliamentary committees have reached the same conclusion: the Lords Constitution Committee in 2006, and PACAC in 2019, both concluded that statute would be too prescriptive, and that a parliamentary resolution offered a better way forward.

What form would a parliamentary resolution take? PACAC included a 300 word draft at para 133 of their 2019 report which read in part as follows:

a convention has become established that Her Majesty’s Government has a duty to inform and consult the House in relation to the deployment of the UK’s armed forces in armed conflict, and to consult and seek prior authorisation from the House before engaging in military conflict, except in the following circumstances…

The exceptions included compromising the effectiveness of UK operations, the safety of British servicemen, the UK’s sources of secret intelligence, or the security or effectiveness of the UK’s operational partners.  They did not include airstrikes or drone strikes alone; but from what we know of Starmer’s thinking, he might want to limit the scope of the convention to the deployment of troops on the ground. That would go against past precedents, several of which have involved parliamentary authorisation of airstrikes; but Starmer would be entitled to put his own stamp on things, since the way the convention has evolved in the past owes as much to policy as to practice.

James Strong has argued that whether parliament gets to have a say depends on four key factors, the first of which is the view held by the Prime Minister of the day, and the last is the nature of the proposed military action. The convention originated in a declaration of principle in 2003, evolved through governmental and parliamentary reports (especially under Gordon Brown) and was recognised in the Cabinet Manual in 2011. For so long as the convention remains as much a matter of government policy as of precedent, it will be liable to change. Successive governments’ concerns for flexibility and executive autonomy have hindered the emergence of a predictable convention. In proposing to limit the need for prior parliamentary authorisation to the deployment of troops on the ground, with the possibility of a subsequent debate in other cases (as happened on 15 January), Starmer could claim that he was introducing greater predictability in the operation of the convention.

But Starmer should not overclaim. An underlying difficulty in codifying the convention is future-proofing it at a time when modern warfare is changing so rapidly. Each time the question arises, warfare has progressed a little further. For example, drone warfare appears to have created a further exception to the convention: there was no parliamentary vote in August 2015 when the UK and US carried out drone strikes in Syria against two ISIS organisers.

The further progression of warfare is well illustrated by the war in Ukraine. With the massive assistance being supplied, it could be said that the UK is already engaging in military conflict, at one remove; and the UK’s armed forces are already deployed, albeit in support and training roles in the UK rather than on the ground in Ukraine. What if the war escalates, and the UK’s engagement with it?  What if Russia uses a dirty bomb, or chemical weapons? And the UK then engages in cyberwarfare, or deploys troops to provide training in Ukraine rather than in the UK? Past precedents give little guidance on whether the convention would necessarily be engaged.

A final observation is that although the convention has depended on the pronouncements and attitudes of successive governments, leading to a wide range of exceptions, parliament and its committees have also played an important role, with six select committee inquiries on the subject in the last 20 years. The process of codification would be better effected by parliament and government together. The Cabinet Manual should reflect the expectations of ministers, but cannot stand alone. At the least, parliament will benefit from further discussion about the role its committees are to play in performing detailed scrutiny, or how (select) parliamentarians might be allowed to examine sensitive material. These committees include not just PACAC and the Lords Constitution Committee, who conducted four out of the six inquiries; but also the Defence Committee, the Intelligence and Security Committee and the Joint Committee on National Security Strategy.

While this does not necessarily require a resolution of the Commons, that would be the ideal solution, ensuring that the codified convention is commonly understood by both parliamentarians and ministers. PACAC’s 2019 report demonstrated a cooperative attitude by parliamentarians, open to making accommodations for the government’s need to keep some matters secret and options flexible. Although the Johnson government was dismissive in its response, a Starmer government might find there is benefit in developing a shared vision with parliament of their respective roles in initiating and approving military intervention of all kinds.

About the author

Professor Robert Hazell was the founder and first Director of the Constitution Unit. 

Featured image: British Army Estonia (CC BY-NC-ND 2.0) by NATO.