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The recent strikes against the Houthis in Yemen have prompted fresh discussions about the UK government’s war powers. Yet in many ways, they have reaffirmed the existing constitutional orthodoxy.

In December 2023, 20 countries gathered to take part in Operation Prosperity Guardian, conducting freedom of navigation exercises off the Gulf of Aden. They did so in response to a series of attacks against international shipping by the Yemeni Houthi rebels, which began with the hijacking of a container ship the previous month. The attacks have caused significant disruption to international trade ever since, sending vessels sailing thousands of miles around the Cape of Good Hope and adding weeks to their journey time.

In early January 2024, after ignoring an ultimatum and attacking allied warships, the Houthis provoked a response. UK and US forces conducted limited, joint strikes across Yemen to ‘degrade the Houthis’ capacity to make further attacks’. More operations followed throughout January and February, with the promise to take additional action, as necessary and appropriate, to address further threats or attacks. Such actions are likely to continue for the foreseeable future.

The strikes have prompted fresh discussions about the UK's war powers, particularly those involving the use of force below the threshold of war. Historically, the role of the legislature has been limited in the UK. Parliament is responsible for passing budgets to finance the armed forces and providing the statutory authority to maintain their existence. Yet the authority to declare and wage war remains a prerogative power vested formally in the monarch.

By convention, this wide-ranging and discretionary authority has been regarded as a ‘political prerogative’, exercised not by the monarch personally, but by ministers of the crown. Over the centuries, the power to make and declare war was gradually transferred from the monarch to their Cabinet, chaired by the prime minister, who possesses the final authority for any decision to use military force without a vote in Parliament. With some notable exceptions, this has been tempered by a long-standing practice of keeping the House informed on war and foreign affairs, offering debates – if not decisions – on these most serious matters of state.

This view was considered orthodox until 2003 when then Prime Minister Tony Blair called an unprecedented, ‘one-off’ parliamentary vote aimed at securing legitimacy for Operation Telic prior to the invasion of Iraq. Rebellious factions within the governing Labour Party threatened to prevent UK involvement, so he framed it as a confidence motion in both his leadership and his government, promising to resign if he lost.

In the event, Blair experienced the largest rebellion within a governing party in a century. His foreign secretary resigned, and he would have suffered a heavy defeat without support from the Conservative benches; only 254 Labour MPs supported the government, far short of the 330 majority needed. Yet a mass resignation of Labour frontbenchers did not materialise, removing the possibility that political pressure would force Blair to resign, and the vote easily passed.

It was suggested that this process established a political rule known as the ‘war powers convention’, whereby, ‘save in exceptional circumstances, the House of Commons is given the opportunity to debate and vote on the deployment of armed force overseas’. Although Blair argued the vote was ‘entirely symbolic’ and ‘non-binding’, both the opposition leader William Hague and successive prime ministers made explicit political commitments to uphold the convention’s spirit. Some even saw it as a stopgap prior to full statutory displacement of the prerogative, an idea prominent, if not dominant, in New Labour circles. Regardless, it has become commonplace to view the debate in terms of a ‘convention narrative’, with Parliament enjoying an ever-greater role in military deployments since 2011, and the prerogative ever-shrinking from view.

As Brown’s 2009 report demonstrated, a statutory war power would be either ‘undesirably broad’ or ‘insufficiently flexible’, fraught with difficulties for little substantive benefit

This was always somewhat illusory. Blair argued that existing practice regarding the prerogative was sufficient. There was no vote on deployments between 2003 and 2011, while a war powers statute was explored and disbanded by Gordon Brown. As Brown’s 2009 report demonstrated, a statutory war power would be either ‘undesirably broad’ or ‘insufficiently flexible’, fraught with difficulties for little substantive benefit. As such, although the prerogative could be put on a statutory footing, there should be good reason for doing so. In the event, Brown argued for strengthening the convention in lieu of legislation.

The convention thus became the only major change to the war powers to survive the Blair-Brown governments, persisting in various guises under David Cameron and Theresa May, albeit subject to an increasing number of caveats and exceptions.

Cameron, an advocate of prerogative reform since 2006, clearly internalised much of the narrative within his understanding of foreign policy. However, his plans for reform never materialised, and his practice was far more telling than his promises. He subjected the 2011 Libyan airstrike campaign, Operation Ellamy, to a vote, winning it decisively. However, operations had already been underway for three days before this was held. When he next sought prior approval for airstrikes against Syria in 2013, he suffered a significant defeat. It proved the first time that any prime minister had been denied the authority to launch military action – authority that, legally speaking, he already had.

In contrast, when Theresa May authorised identical airstrikes against Islamic State in 2018, she preserved the substance of the convention while reinterpreting it. Relying partly on the framework set out by Cameron’s defence secretary, Michael Fallon, May launched strikes without a debate, arguing their ‘emergency nature’ precluded consultation. She merely asserted that she was observing the convention, and that her government was acting within the framework that had been set out, even while reinterpreting its bounds to enlarge their scope.

This chequered history has led many to revise their position on the convention. Consensus suggests it exists in a state of limbo. Others have gone further, arguing it no longer exists in practice.

This is certainly true if one views it through the lens of the ‘convention narrative’. From this perspective, the government has evaded Parliamentary scrutiny through novel reinterpretations of its authority to act. Moreover, by refusing to displace the prerogative by statute, its actions remain effectively unconstrained.

The problem is that the convention narrative presents an inaccurate picture of the prerogative. Past practice can help contextualise this. The convention has always been driven by the judgement of the prime minister as well as the authority they command in the House. Blair and Cameron chose to put their use of the war powers to a vote because their authority on these issues was relatively weak. Blair struggled to unite the sceptical left wing of the Labour Party around the idea of intervention, while Cameron’s coalition with the Liberal Democrats would probably have collapsed without a vote. The choice to put these issues to Parliament reflected both the fragile politics sustaining their governing coalitions and their own judgement of the proper relationship between Parliament and the prerogative. In the end, Blair convinced a significant majority to back his decision, while Cameron put forward a weak case and mishandled his political strategy, struggling to make the case for UK involvement.

When seen in context, the convention narrative looks rather thinner than its advocates suggest

However, whenever the convention has been reinterpreted, the government has possessed a strong or united majority in Parliament, and could be confident of victory even if a vote was held. Operation Ellamy is the outlier, though Cameron avoided the dilemma faced by Blair in 2003, as he had international authority to act. He took strike actions over the weekend and held both a debate and a vote the following Monday, in line with what the House expected post-Iraq. The Syrian airstrikes in 2018 and the recent strikes against the Houthis were both initiated over weekends, yet debates were held the following Monday also. The first was a light-footprint operation without UK troops, the second a direct response to an attack on the Royal Navy. Neither proved controversial in the aftermath.

None of this came at the expense of the convention. On the contrary, every prime minister since Blair has framed their actions in its terms, even when responding to novel circumstances. May asserted she had acted within its limits and worked hard to prove it, outlining a strong framework for the future exercise of the prerogative. Had she appealed to Parliament in 2018, she would likely have received the support she sought. The Conservatives enjoyed a slim majority, and divisions between opposition leader Jeremy Corbyn and his backbench MPs, many of whom supported intervention, led to rifts within the Labour Party which May could probably have used to gain cross-party support. However, she chose not to put this to the test. It was a gamble that turned on her own political judgement, and which ultimately paid off.

When seen in context, the convention narrative looks rather thinner than its advocates suggest. Yet this should come as no surprise. The range of military actions the government can take varies widely, and the executive is afforded room to interpret what counts as emergency action, as well as broad discretion to act in defence of protect critical national interests. These determinations rest with the prime minister and Cabinet, who assess, interpret, and authorise the use of force. Although the perceived erosion of the convention has led to calls for a US-style War Powers Act, this has remained a fringe position for reasons beyond those in the Brown report.

First, owing to the principle of parliamentary sovereignty, any government which enjoys a cohesive enough majority in the Commons to ignore the substance of the convention could, by extension, overturn any War Powers Act intended to limit its authority. It would have to expend political capital to do so, but no more than a government seeking to ignore the current practice around the convention itself would.

Second, and more importantly, the US experience refutes the assumptions of the convention narrative. The US president has been nominally constrained by the War Powers Resolution since 1973. Passed as a reaction to the Vietnam War, this statute was aimed at restricting the executive’s unilateral authority to wage war without Congressional involvement. While it has succeeded in preventing Vietnam-style creeping escalations, and although presidents have consistently sought Congressional approval before the major deployment of ground forces, it has fallen substantially short of its legislative intent. Noted for its own unhappy history and failure to live up to expectations, successive Republican and Democrat administrations have frustrated its provisions, adopting creative interpretations of reporting requirements and the phrase ‘hostilities’ to authorise extended campaigns beyond statutory time limits. When pressed, presidents have argued that their actions are merely ‘consistent’ with the Resolution’s requirements, refusing to acknowledge that they take action under its authority, and asserting the statute is an unconstitutional infringement on their office.

The most important element of the Resolution hinges on the 60–90 day time limit within which a president must withdraw US troops they have committed to hostilities, unless Congressional approval is granted to extend this. For the Houthi action, this was triggered when the Biden administration submitted its first War Powers Resolution report on 12 January, notifying Congress that strikes were conducted alongside the UK pursuant to the president’s authority as Commander-in-Chief, in accordance with the conditions of the Resolution. This would theoretically limit the duration of the campaign to 12 April, at a maximum.

However, Biden has already laid the groundwork for extending the campaign beyond this formal window. The administration has submitted a series of reports for each joint action with the UK, but none for strikes conducted without UK involvement. This has led many to speculate that Biden will continue the practice of claiming the 60-day time limit resets with each new report, or else that the US is not technically involved in ‘hostilities’. The Resolution’s substantive constraints are, despite appearances, quite limited in practice.

The Houthi case highlights the fact that debates and votes have been used as tools to overcome issues of authority and legitimacy

Given all of this, what do the recent Houthi strikes say about the war powers in the UK today? In many ways, they reaffirmed the old constitutional orthodoxy. Both the prime minister, Rishi Sunak, and opposition leader Keir Starmer unequivocally stated that the actions were conducted in accordance with the convention framework and past precedent. However, the prime minister also noted that:

Fundamentally, we need to