Why can the prime minister still take Britain to war without a parliamentary vote?

The UK parliament is one of the weakest in the democratic world on military action: no vote or even notification is required. 

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On the matter of war, few western parliaments are weaker than Britain’s. There is no legal requirement for the prime minister to consult MPs before taking military action, or even to inform them.

In recent days, Conservative MPs and Tony Blair have emphasised that Theresa May would not require parliamentary approval to launch air strikes against Syria following last week’s chemical weapons attack. How has this antiquated power endured?

In 2007, shortly after entering No 10, Gordon Brown vowed to limit the Royal Prerogative under which the prime minister can unilaterally declare war. Parliament, Brown proposed, would be guaranteed the right to approve “significant, non-routine” deployments of the armed forces to “the greatest extent possible”. But absorbed by the 2008 financial crisis and the recession that followed, the government abandoned reform. 

Some argued that the 2003 Iraq war vote (which prompted the largest backbench rebellion since the 1846 repeal of Corn Laws) had established an informal convention by which MPs would be consulted in advance of military action. But an exception was made in the case of the Libya intervention in 2011, which parliament only approved retrospectively (with just 13 MPs rebelling), and in Mali in 2013 (no debate or vote was held).

The Commons did, of course, defeat the government over military action in Syria in 2013 - the first time a prime minister had lost such a vote since 1782. Ed Miliband has since been praised by some and denounced by others for “preventing war - but the irony is that Labour did not expect to win the vote and that it was surprised when Cameron ruled out any intervention (the prime minister may well have won a second vote).

In 2014, MPs were consulted on - and supported - air strikes in Iraq against Isis. Yet the 2013 commitment made by then foreign secretary William Hague to “enshrine in law for the future the necessity of consulting Parliament on military action” was never fulfilled.

There is, nevertheless, now an expectation that MPs will be consulted before significant British military action, though not in emergency situations. Special operations, such as the 2015 strike against Mohammed Emwazi in Raqqa, are also not pre-approved by parliament.

The difficulty, as so often with Britain’s unwritten constitution, is a definitional one: what qualifies as “significant military action” or an “emergency”? MPs reasonably fear that an unscrupulous prime minister could use the ancient Royal Prerogative to bypass them.

A 2010 survey of 25 European democracies found that 11 had “very strong” parliamentary war-making powers: “Prior parliamentary approval required for each government decision relating to the use of military force; parliament can investigate and debate use of military force.” Four countries had “strong” powers (prior approval of military action in all but exceptional circumstances), two had “medium” powers (the ability for parliament to demand troop withdrawal and to investigate and debate military force) and four had “weak” powers (parliamentary notification required). Only four countries (the UK, France, Cyprus and Greece) had “very weak” powers: no parliamentary approval or debate required.

As British prime ministers, haunted by the spectre of Iraq, have become ever more reluctant to commit forces abroad, the debate over war-making powers has receded. But as MPs prepare to notionally “take back control”, they may ask why they have so little over the gravest issue of all. 

George Eaton is political editor of the New Statesman.