The UK Parliament’s Syria vote offered (and lost) by David Cameron in 2013 suggests that former Prime Minister Tony Blair may have left a remarkable constitutional legacy as a result of the Iraq war – one that affects the United States and possibly even France as well as Britain. Even though British Prime Ministers can declare war and deploy troops abroad under Royal prerogative without any Parliamentary approval, in 2003 Blair sought the backing of Parliament for the Iraq venture. For the first time since the 1950 Korean conflict Parliament had a say (albeit “consultative”) prior to the engagement.
So what is the history of the prerogative power to make war, and has Britain now created a new constitutional precedent that amounts to a new convention?
The prerogative power to make war is one of a number of monarchical powers retained by the Crown as the medieval representative parliamentary system (which began as a means of legitimising tax-raising beyond the Crown’s traditional levies, particularly for wars) grew into a qualified democracy. Those prerogative powers that remain (including appointing governments and the dissolution of Parliament – until the change in the Coalition agreement in 2010) are mostly held by the Prime Minister in the name of the Crown and the relevant Secretaries of State: the Defence Secretary for war-making, the Foreign Secretary for treaty-making and regulating foreign relations (though treaties often have a parliamentary passage of some sort; see below). The Executive (Government) decides on military deployments, not the Legislature (Parliament).
The US President is Commander in Chief of the Armed Forces; the UK Prime Minister derives his/her powers from the Queen who is also Commander in Chief. The fiction is that the Queen’s powers are not exercised by the Prime Minister and Secretaries of State as such but that she is likely to be bound by their advice on such matters so they in effect hold the power.
‘Methinks it’s a very strange thing for a king to consult with his subjects what war he means to undertake. This were the means for his enemies to know what he intends to do’ – Commons Speaker, 1621