Towards the codification of war powers?

By: David Klemperer

Last month, Rishi Sunak’s decision to conduct airstrikes against the Houthis in Yemen sparked significant debate – not only about the merits of such actions, but also about their constitutionality. Several opposition politicians – including Scottish First Minister Humza Yousaf and former Labour leader Jeremy Corbyn – suggested that the Prime Minister ought to have recalled Parliament, and to have sought the approval of the House of Commons before authorising military action. This was no one-off dispute. Rather, the controversy taps into a longer running debate about the war powers of UK governments, the role of Parliament, and whether constitutional codification is needed. 

The constitutional basis for military action

Currently, the constitutional position is clear: the decision to use the Armed Forces is a royal prerogative power, exercised by the Prime Minister and the cabinet on behalf of the crown. Although the Government is ultimately accountable to Parliament, Parliament itself has no formal role in authorising military deployments. Rather, the Government is empowered to act upon its own initiative, without having to seek any specific approval. Sunak thus had no legal obligation to recall Parliament, or to hold a parliamentary vote. It is worth noting that this is not a particularly unusual state of affairs amongst European democracies: although in some countries, such as Germany, the Government has to seek prior parliamentary approval to use military force, in others, such as France, the situation is much the same as in the UK, with the Government able to act without seeking either prior or ex post approval from the legislature. 

However, in the early twenty-first century a convention emerged that governments should seek parliamentary approval before undertaking military action. This began in 2003, with the decision of Tony Blair’s Labour Government to hold a parliamentary vote on UK participation in the Iraq War – a vote the Government won by 412 to 149. Although originally intended as a one-off concession, it soon produced a cross-party consensus that it had established an important precedent. After the Conservative-Liberal Democratic Coalition came to power in 2010, this consensus was established as a convention. David Cameron’s Government formally acknowledged that “A convention has developed in the House that before troops are committed, the House should have an opportunity to debate the matter”, and inserted this line into the 2011 version of the Cabinet Manual. As a result of this new convention, the House of Commons was consulted on military action four times between 2011 and 2015, on interventions in Libya, Iraq, and Syria. Most notably, in August 2013, Cameron recalled Parliament to hold a House of Commons vote on a planned intervention in Syria; when the vote went against intervention (by 272 to 285), Cameron agreed to respect the will of the Commons, and to call off military action. 

Since the end of Cameron’s premiership however, the constitutional pendulum has swung back. In April 2018, Theresa May ordered airstrikes against Syria (of a kind similar to those that Parliament had rejected under Cameron in 2013) without seeking parliamentary support, and justified her decision by citing operational necessities; when Labour tabled a motion condemning her circumvention of Parliament, it was rejected by MPs. In October 2019, when the House of Commons Public Administration and Constitutional Affairs Committee (PACAC) suggested a greater role for Parliament in authorising military action, the Boris Johnson Government responded dismissively, suggesting that “the current arrangements provide the appropriate balance between Parliamentary scrutiny and operational flexibility”. Now, in 2024, Sunak (with Cameron as his Foreign Secretary!) has followed May’s precedent in seeking neither prior nor ex post parliamentary approval, and in justifying his decision with reference to operational needs. 

In many ways, this reflects a broader shift in constitutional attitudes that has taken place in recent years. Whereas both New Labour and the Coalition pursued constitutional policies designed to constrain and diffuse the power of central government, Conservative governments since Brexit have preferred to reinforce the power and autonomy of the executive. This then raises the question: if (as looks likely) the Labour wins the next general election, might a Keir Starmer Government take a different approach? 

Keir Starmer and the codification of convention 

In his 2020 Labour leadership campaign, one of Starmer’s ten pledges was to introduce a “Prevention of Military Intervention Act”, which he described on The Andrew Marr Show as “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”. This was not a new idea: Starmer’s predecessor as Labour leader, Jeremy Corbyn, had previously called for a “War Powers Act” along similar lines, while in 2016 Baroness Falkner unsuccessfully introduced a War Powers Bill in the House of Lords. (Moreover, from 2007 until 2016, the eventual introduction of a War Powers Act was officially Conservative Party policy.)

Today however, Starmer appears to have retreated from this position somewhat, supporting Sunak’s decision to carry out airstrikes in Yemen, and refraining from criticising the lack of parliamentary consultation on the basis that the situation was urgent. However, in an interview with Laura Kuenssberg, Starmer insisted that he does still wish to strengthen Parliament’s role, specifically with regard to deployments involving ground forces:

“The Foreign Secretary when he was Prime Minister really established the convention that if there is going to be a sustained campaign, if there are going to be troops on the ground … there has to be viable case, and that should be put before Parliament … and there should be a vote … I want to codify that it could be in a law or it could be by some other means.”

In other words, Starmer has expressed the intention to formalise the convention acknowledged by Cameron in 2011 and inserted into the Cabinet Manuel – albeit on a narrower basis, applied only to “sustained campaigns”. The aim would appear to be to secure the precedent established by the vote on the Iraq War, without extending it to the kinds of more limited military actions that now seem to be the norm when it comes to the UK’s foreign interventions.  

What might such codification look like? Crucially, Starmer’s comments suggest that it would not necessarily have to be done via statute and could be done “by some other means”. This reflects a growing consensus amongst both politicians and constitutionalists: in 2019, the PACAC report echoed an earlier report of the House of Lords Constitution Committee in concluding that attempting to put the Government’s war powers on a statutory basis would be unwise: 

We are persuaded by the evidence that any attempt to legislate for all possible contingencies and exceptions would lead to unintended and unfortunate consequences, including the unwelcome possibility of judicial review of government decisions as well as legal action against members of the Armed Forces and consequent uncertainty in relation to the deployment of military force, which could be detrimental to the national interests.

However, the report did suggest that the convention could still be formalised via the passage of a resolution in the House of Commons, specifying the relationship between the Government and Parliament in relation to decisions to take military action. Although not legally enforceable, it would be a means for the House of Commons to make clear what it expects from the governments to which it accords its confidence when it comes to the use of the Armed Forces. Notably, this was the approach abortively pursued by the last Labour Government in its proposed “Governance of Britain Reforms” before it left office in 2010. Given Starmer’s stated commitments, it may well also be the next Labour Government’s approach. 

David Klemperer.

David Klemperer is a PhD candidate in History at Queen Mary University of London, and a former Research Fellow at the Constitution Society.

The Constitution Society is committed to the promotion of informed debate and is politically impartial. Any views expressed in this article are the personal views of the author and not those of The Constitution Society.