The UK Foreign Secretary, Boris Johnson, recently informed BBC Radio 4 of the possibility of UK military action against Syrian Government forces if the US invited the UK’s support. However, he added, whether the Government can take such action without seeking Parliamentary approval ‘needs to be tested’. Action against the Syrian Government would not be covered by the two Parliamentary approvals for airstrikes against so-called ‘Islamic state’ in both Syria and Iraq: accordingly, such a deployment squarely raises the question of whether Parliamentary approval is required for the use of military force.
Constitutional conventions in the UK
Constitutional conventions are defined by Dicey as the ‘understandings, habits, or practices’ that ‘regulate the conduct of the several members of the sovereign power, of the Ministry, or of officials.’ One of the critical features of conventions is that, although they lack legal robustness, they are treated as binding by the constitutional actors to whom they apply. The fact that conventions are ‘habits or practices’ means that they are not created, but crystallise over a period of time.
conventions are seen to embody a principle of ‘constitutional morality’
The determination of whether a convention exists depends on the well-known Jennings Test:
- What are the precedents (i.e. the previous occasions on which individuals have acted compatibly with the convention)?
- Did the actors in those cases believe that they were bound by the relevant convention?
- Is there a sound reason for the convention?
Constitutional conventions are not legally enforceable. Recognition of a Convention by an Act of Parliament does not automatically make the convention enforceable: this principle was recently articulated by the Supreme Court in R (Miller) v Secretary of State for Exiting the European Union  UKSC 5 in relation to the Sewel Convention, despite its recognition by the Scotland Act 2016.
However, because conventions are seen to embody a principle of ‘constitutional morality’, actors feel bound by them. But it appears that conventions may be breached without any major consequences if the convention (and the ‘moral principle’ underlying it) is considered marginal or insignificant; alternatively, the relevant actor may argue that the particular situation justifies an exception to the general normative force of the convention.
The constitutional position regarding military action
The UK constitutional position regarding military action has a rich history. Before 2003, and barring a few exceptions (Prime Minister Attlee went to the House of Commons to vote on the Korean War, and there was a brief period during the English Civil War where Parliament exercised the war prerogative), the power to deploy troops was placed firmly under the Royal Prerogative.
Until recently, the historical position was consistent enough to allow Lord Reid to observe, in Chandler v DPP  AC 791, that ‘It is my clear opinion that the disposition and armament of the armed forces are and for centuries have been within the exclusive discretion of the Crown.’
Developments from 2003 onwards
Critically, however, that position changed in 2003 with the emergence of what is now generally accepted to be a convention requiring the UK Government to seek approval from the House of Commons for any proposed military action.
the then Prime Minister, David Cameron, honoured Parliament’s vote despite not being legally obliged to do so
This convention can be traced to the decision of Tony Blair, somewhat reluctantly, to invite Parliament to vote on whether to invade Iraq in 2003. This precedent was then applied in 2011, when Parliament voted on the proposal for British forces (as part of NATO) to enforce a no-fly zone over Libya, and was finally established when Parliament refused to permit air strikes in Syria in 2013, following claims that the Assad regime had deployed chemical weapons. Firmly establishing the force of the emerging convention, the then Prime Minister, David Cameron, honoured Parliament’s vote despite not being legally obliged to do so.
Subsequent votes to conduct airstrikes in Iraq in 2014 on invitation by the Iraqi government, and in Syria in 2015 (though importantly, only against so-called ‘Islamic State’ targets), have arguably consolidated the convention. Despite the genesis of Parliament’s consultative role in 2003, therefore, only from 2013 did a consistent practice materialise that crystallised the practice (especially as non-combative military interventions, such as in Mali in 2013, had taken place without Parliamentary approval in the meantime).
The current UK constitutional position on deployment decisions, accordingly, is that the Government will seek the approval of the House of Commons for military action in which UK armed forces are to be deployed in a combative capacity. Presumably, initially non-combative deployments which subsequently become combative (known as ‘mission creep’) would also require subsequent Parliamentary approval.
Parliament has no power to initiate military deployments; there is also a lack of standards setting out the type and level of detail of information which the Government should supply to Parliament in order to allow it to decide whether to approve a particular deployment. Despite these limitations, however, the strength of the convention is enough to suggest that ‘Parliament now decides when Britain goes to war’.
Limitations of the newly-emerged constitutional convention
Though leading commentators have interpreted this newly-emerged constitutional convention as a strong one – particularly following David Cameron’s compliance with the vote of the House of Commons in 2013 – the precariousness of conventions as legally non-binding and non-justiciable is apparent in the Foreign Secretary’s recent comments.
a lack of Parliamentary consultation may not disrupt or destroy the convention in respect of future military action
The contingency of a convention’s establishment – relying upon consistent practice – would mean that a significant departure from it would risk undermining its careful and tentative development. If Boris Johnson and the UK Government were to circumvent Parliamentary involvement in fresh air strikes on Syria, it is not clear that the convention would survive.
However, a lack of Parliamentary consultation may not disrupt or destroy the convention in respect of future military action if the circumstances fell within the scope of an established exception. It is currently understood that Parliamentary approval may be circumvented to protect critical national interests, prevent humanitarian catastrophe, or in self-defence. We will have to wait and see whether the Government seeks to apply one of these three exceptions in order to justify military action against the Syrian Government without Parliamentary consultation, or whether it seeks to enlarge the class of exceptions.
Looking to the future
Although Parliamentary approval of military deployments is arguably a tenuous check on what would otherwise be an unbridled exercise of executive power, it provides at least some protection against unilateral military action (evidenced by interventions in Kosovo, Afghanistan, Iraq, Libya and Syria). The Foreign Secretary’s suggestion that Parliament may be circumvented is, therefore, a very worrying step.
However, the Prime Minister recently contradicted the Foreign Secretary by stating that new strikes would be voted upon, and the Labour Shadow Minister for Peace and Disarmament, Fabian Hamilton, has made a proposal to enshrine Parliament’s role in law. Such legislation would render this emerging convention a statutory reality, and may even raise the possibility that such decisions could be reviewed by the courts.