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What is Parliament’s constitutional role in approving military action?

The decision to deploy the Armed Forces in situations of armed conflict is a prerogative power, exercised by the Prime Minister on behalf of the Crown.

In constitutional terms Parliament has no legally established role in approving the deployment of the armed forces and the Government is under no legal obligation with respect to its conduct in such situations, 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 it is accepted that it would be politically difficult to engage in military action without parliamentary support

The 2011 convention

In 2011 the Coalition Government acknowledged that 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” (PDF).

As the convention has evolved, successive governments have defended this “emergency caveat” and made clear the Government would 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.

There has been longstanding debate over what might constitute an emergency or critical national interests, given the lack of established definitions, and therefore, the government retains considerable discretion when it comes to meeting the obligations of the convention.

Despite the convention, it also remains the case that Parliament has no legally established role in approving the deployment of the Armed Forces.

The basis for military action in Yemen

The UK Government said the strikes on Houthi positions in Yemen on 11 January 2024 were “limited, necessary and proportionate in self-defence”. In a summary of the Government’s legal position, the government said action had been taken under Article 51 of the UN Charter.

This military action was taken without prior recourse to Parliament. Armed Forces Minister, James Heappey, said that the Government had to “make decisions such as these based on the military, strategic and operational requirement” and this led to the timing of the operation. He said the Commons could discuss the issue when it returned on Monday 15 January.

Does the government’s approach have a precedent?

The last time the UK committed military forces to action overseas was in April 2018, when strikes were conducted against the Syrian regime’s chemical weapons facilities.

That action was justified on humanitarian grounds and taken without prior recourse to Parliament. The decision was also not subject to a retrospective vote.

The Government defended its approach, saying that “it was necessary to strike with speed so we could allow our Armed Forces to act decisively, maintain the vital security of their operations, and protect the security and interests of the UK”.

In a statement to the House of Commons on 16 April 2018, the Prime Minister also defended the decision to take action without prior parliamentary approval, suggesting that MPs had been given the chance to debate the issue at the first opportunity.

What about previous decisions to deploy the armed forces?

While the decision making around the strikes against Syria in 2018 did not involve the approval of Parliament, since the emergence of the convention in 2011 there have been several other deployments which Parliament has expressed its view on. However, the government’s approach to consulting Parliament has not been consistent:

All of these instances are examined in greater detail in Library research briefing, Parliamentary approval for military action, 2018.

How have parliamentarians responded?

Labour Party leader, Keir Starmer has backed the strikes on Yemen and called on the Prime Minister to make a full statement to Parliament. Former Shadow Chancellor John McDonnell argued on X (formerly Twitter), however, that parliamentary approval should have been requested first.

This is a position shared by the Scottish National Party. SNP leader Humza Yousaf said: “Before action was taken, the correct and appropriate thing to have done would have been to have recalled parliament, who have given serious detail about any proposed military action”.

Liberal Democrat spokesperson for foreign affairs, Layla Moran called for an immediate recall of Parliament and a retrospective vote.

Plaid Cymru MP Liz Saville Roberts has criticised the decision to conduct strikes without parliamentary scrutiny.

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