Documents to download

This briefing paper has been replaced by another research briefing paper: Military action: Parliament’s role, April 2024.

This briefing remains useful for the historical context, international comparisons and the detail of past reform efforts.  

The Royal Prerogative

The decision to deploy the Armed Forces in situations of armed conflict is currently a prerogative power. In the event of a declaration of war or the commitment of British forces to military action, constitutional convention requires that authorisation is given by the Prime Minister, on behalf of the Crown. Decisions on military action are taken within the Cabinet with advice from, among others, the National Security Council and the Chief of the Defence Staff.

In constitutional terms Parliament has no legally established role and the Government is under no legal obligation with respect to its conduct, including keeping Parliament informed. In practice however, successive Governments have consulted and informed the House of Commons about the decision to use force and the progress of military campaigns, although there has been little consistency in how that has been achieved.

Nor is the Government under any constitutional obligation to abide by the result of any Parliamentary vote on military action, although in reality it would be politically difficult to engage in military action without Parliamentary support.

Pressure for reform

Since 2003, and the decision to allow Parliament a vote on military action in Iraq, there has been increasing pressure for reform. In 2007 the Labour Government announced a package of constitutional reforms intended to strengthen democracy and accountability and establish a new relationship between the Government and the people. Among suggested reforms was the proposal that a resolution of the House be passed giving Parliament the right to approve “significant non-routine” deployments of the Armed Forces, albeit “to the greatest extent possible” and “without prejudicing the Government’s ability to act to protect national security, or undermining operational security or effectiveness”. Those proposals were never implemented before the Labour government left office in 2010.

2011 parliamentary convention

In 2011 the Coalition Government suggested that, since 2003, a convention had emerged in Parliament that before troops were committed to military operations the House of Commons should have an opportunity to debate the matter. It also proposed to observe that Convention except when there was an emergency and such action would not be appropriate.

While the convention was broadly welcomed, there was some initial debate as to whether such a parliamentary convention could be said to exist. Between the Iraq vote in 2003 and the Government’s observations in March 2011 there had been no Government-tabled debate, or vote, on any deployment of the Armed Forces, including the commitment of significant numbers of British forces to Helmand province in Afghanistan in 2006. Even the deployment of forces in Libya, which happened in concert with the Government’s acknowledgement of the convention in March 2011, was not the subject of a prior parliamentary debate and vote, which led Professor Gavin Phillipson at Durham University to argue that Libya was “not a fully satisfactory precedent” for parliamentary approval.

In a May 2011 report the Political and Constitutional Reform Committee called “for greater clarity on Parliament’s role in decisions to commit British forces to armed conflict abroad” and recommended that the Government work toward formalisation of the process, initially through the adoption of a parliamentary resolution, but with a view to the introduction of legislation in the longer term.

Evolution of the convention

The first deployment of British military assets after the Libya campaign was in Mali in early 2013. That deployment was undertaken without any debate, or vote in Parliament which drew some criticism given the Government’s previous assurances, and once again raised questions over the credibility of the convention and what sort of deployments would be likely to trigger its use.

By the end of 2015 Parliament had been given the opportunity to debate, and vote, on the deployment of British forces on three further occasions. The first was in response to the alleged use of chemical weapons against civilians by the Assad regime in Syria in August 2013, the second was in response to the actions of Islamic State (ISIS) in Iraq in September 2014 and the third was to seek approval for extending military against ISIS into Syria in December 2015.

The Government motion to deploy military forces in Syria in 2013 was defeated by 13 votes. Despite its defeat the Government stated that it would respect the will of the House, a move that was widely viewed as an assertion of Parliamentary sovereignty and a direct challenge to the Royal Prerogative on such matters. It also led many commentators to suggest that any future significant deployment of the Armed Forces would now be inconceivable without prior recourse to Parliament.

That view gained further credence following the decision to seek parliamentary approval for offensive military action against ISIS in Iraq in September 2014 and to extend that action into Syria in December 2015, in line with the newly adopted convention. On both occasions the House supported the deployment of military forces.

Has clarity been achieved?

The Syria vote in 2013 was, and continues to be, viewed by many as a turning point in the debate on parliamentary approval. Commentators have argued that the defeat of the Government laid to rest doubts over the convention’s existence and made the deployment of the Armed Forces without parliamentary approval, politically difficult in the future.

Yet, has clarity on the use of the convention been achieved? The issue appears to have evolved from the question of whether the convention exists at all, to one of when it will be triggered. On the basis of recent deployments a nominal threshold for parliamentary approval appears to have been established:

  • The possibility of premeditated military action exists.
  • Military forces are to be deployed in an offensive capacity.

Under the Convention, as it has developed, it has been made clear that the Government would also come to the House retrospectively in emergency situations, where there was a need to protect a critical British national interest or to prevent a humanitarian catastrophe. If the House is dissolved the Government would also come to Parliament as soon as possible for a parliamentary debate on the matter. However, the Convention does not explicitly commit the Government to a vote in such circumstances, merely the opportunity to debate the issue.

As many commentators have also observed, the spectrum of potential military operations is vast and ‘critical national interests’ can be broadly interpreted. The lack of established definitions therefore continues to cause unease for many, and has led several to argue that the Government retains considerable discretion on what meets the convention’s threshold thereby making the whole framework potentially open to interpretation and exploitation.

Indeed, military action taken against the Syrian regime’s chemical weapons facilities on 14 April 2018 was done without recourse to Parliament. The Government has justified its actions on humanitarian grounds.

In a Statement to the House on 16 April 2018, the Prime Minister defended the decision to take action without prior parliamentary approval, suggesting that MPs had been given the opportunity to debate the issue at the first opportunity. However, a retrospective vote approving military action was not forthcoming. Unlike the Libya campaign in 2011, these latest airstrikes are not the start of a sustained military campaign but have been described by the Government as a “limited, targeted and effective strike with clear boundaries”. A vote was held at the end of a subsequent emergency debate on Syria, however that vote was called by the SNP on the Question: “That this House has considered the current situation in Syria and the UK Government’s approach”. It was not approval for the deployment of forces.

For many, the Statement and subsequent debate on 16 April 2018 arguably fulfils the Government’s commitments under the Convention. For others, however, it is the first direct challenge to the Convention’s credibility and has subsequently reignited the longstanding debate on placing Parliament’s role on a formal statutory footing

Prospects for formalising Parliament’s role

Despite the emergence of the Convention it remains the case that Parliament has no legally established role in approving the deployment of the Armed Forces. A commitment to legislate was made by the then Foreign Secretary, William Hague, in 2011. By the end of the 2010-2015 Parliament no legislative proposals had been put forward by the Government, which suggested that the imperative is to consider the issue properly “rather than being driven by an artificial deadline” and that given its commitment to observe the convention, “the case for urgency has not been established”.

The lack of progress on this issue remained a concern for many observers, most notably the Political and Constitutional Reform Select Committee who have long argued for Parliament’s role to be placed on a statutory footing. Several commentators, including the Committee, have called for an interim parliamentary resolution in order to “clarify some of the ambiguities that exist under current arrangements. Others have suggested that a resolution alone would address the issue of formalisation whilst also avoiding some of the complexities associated with legislation.

In April 2016 the Government announced that it would no longer seek to legislate on this issue in order to “retain the ability of this and future Governments and the armed forces to protect the security and interests of the UK in circumstances that we cannot predict, and to avoid such decisions becoming subject to legal action”.

The problems of formalising Parliament’s role

Defining either a resolution or legislation in a way provides Parliament with a meaningful role, yet safeguards the Government and military’s capacity to act, is paramount. Yet it is fraught with difficulties and potentially raises more questions than it resolves. One of the main problems is that of definition and how to adequately define the sort of military action that would trigger Parliamentary involvement; under what circumstances the Government could invoke the “emergency caveat”; and whether the escalation of an operation should require fresh approval. Parliament’s access to information, including legal advice and intelligence, prior to making a decision would also have to be carefully set down. Placing Parliament’s role on a statutory basis also raises issues of justiciability and the potential for legal challenge in the courts.


One of the biggest challenges in moving beyond the current convention is that all stakeholders, even within Government, have differing opinions on what they want a resolution or legislation to achieve. This dilemma also lies at the heart of the current convention and is one of the reasons advocates are pushing for a more formalised solution. There are no right or wrong answers and possibly this circle will never be squared. Achieving a solution acceptable to all will require immense political will and, as such, makes the continuation of the current convention a much more likely prospect for the foreseeable future.

Documents to download

Related posts