The Royal Prerogative occupies an crucial space in the national consciousness and legislature. In his awesome book The Monarchy and the Constitution, Vernon Bogdanor locates the authority of the Crown in its emotional resonance, a direct consequence of the Crown's wholly non-executive role ("a set of conventions have limited the discretion of the sovereign so that his or her public acts are in reality those of ministers"). The Crown may, by law, ‘exercise discretion’ to any measure it wishes. Hold on, it’s less stupid than that. In truth, the Crown has only three ‘rights’, as Bagehot wrote; ‘the right to be consulted, the right to advise, and the right to warn.’
Other countries have other figureheads; the best example is the US and their Constitution. President Ciampi, for example, garnered only a fraction of the Queen's affection, with only a few more executive functions. We’re a parliamentary democracy; our figurehead is a single person. This 'symbol', the Crown, is at once separate from and yet an embodiment of the democratic process.
Bogdanor goes on to say that the most important role the Queen fulfils is exercising discretion as a 'guardian of the constitution' - when she deems there to be deviance from it, she is to ensure that 'the values that lie at the foundation of a constitutional system are preserved'. "The doctrine that the sovereign is required to act on the advice of ministers presupposes that ministers themselves act within the framework and presumptions of constitutional government". The Monarch is meant to be a disinterested arbiter, watchfully exercising some kind of Robespierrean and arbitrarily devised 'constitutional will'.* There’s a paradox here. While the Crown appears to be subordinate to the executors of the constitution, she is also its ultimate guarantor and executor - executively non-executive? If our ultimate democratic safeguard is a non-democratic function, are we, eventually, functionally non-democratic?
The idea, basically, is that the Monarchy is like Democracy’s fuse. If things get out of hand, the monarchy goes first; only an issue deemed to be more important than Republicanism could bypass this effect. And in England, at least, I don’t think anything would raise quite the hell that sacking that lot would. So, really, it works.
This established, what are the problems for the future? I think that it’s inevitable that more constitutional legislation will be passed, and that, like urban sprawl, this will chip away at the countryside of the Royal Prerogative by writing it in. The point of the Royal Prerogative is that it is unwriteable. And hardcore constitutionalists prefer shall to may. And any formalization is a restriction. Now, I’m all for an anti-democratic safeguard of democracy: what about a council of nine appointed for life by whichever executive was in power on an as-and-when basis? I just don’t think it’d catch on, though – who’d take it seriously? Till then, the Royal Prerogative is all we’ve got.
* Cletus_the_Fetus points out that that this metaphor is counterproductive to what I'm trying to say: that Robespierre was a reaction against Louis XIV's "l'etat, c'est moi", and that the resason that the British Monarchy's powers are as they are is because in Britain we never want to need a Robespierre (as Earl Grey said in 1831, we need to "prevent the necessity for revolution"). This means that though, yes, Robespierre and the Queen both interpret mandates acquired in the vaguest of ways if at all, comparing the constitutional good to the public good is misleading. Robespierre has contributed in no small measure to the UK consitutional understanding. So I probably shouldn't mix things up by taking his name in allusive vein. There's an implicit causal fallacy, or something. Thanks, Cletus.
Robert Blackburn, The Electoral System in Britain
Vernon Bogdanor, The Monarchy and the Constitution