@escoville: If you still care about this question (after our lengthy discussion!), this might be of interest.
Source: "Royal Assent to Legislation." The Law Quarterly Review 129, no. Apr(2013). Author: Rodney Brazier, MVO, LLD, FRHistS, Emeritus Professor of Constitutional Law, University of Manchester. (Article sent to me by the author.)
An excerpt from the article:
Royal assent is part of the royal prerogative, which is part of the common law. No part of the common law loses its legal effect through desuetude. The earlier examination of the concept of the Queen in Parliament shows beyond doubt that the royal veto power, as a matter of law, remains. It follows that the veto itself, in law, could not be removed without royal assent to a Bill written for the purpose – which, of course, a Sovereign could, in law, veto. (If the veto were so used, what a constitutional crisis that would be.) The courts have never had to adjudicate on the prerogative power to grant or withhold royal assent, and so there is no case-law guidance about its use.
The next point about the veto, of course, concerns the conventional position. No one disputes the existence of what may be termed the cardinal convention of the British constitution, which is that the Sovereign must normally act on ministerial advice. The Government will recommend the granting of royal assent to every Bill passed by Parliament, regardless of its type. But even those today who are the most sceptical about the extent of royal constitutional power recognise that, at least as far as legislation is concerned, that convention does not require royal assent to be given automatically, and that there must be exceptions which would permit the use of a veto. We know that the last Sovereign seriously to consider a possible veto was George V in 1913–1914 over the Home Rule Bill, but in the event he fell in with his Government’s wishes.
... In the result, while the legal power to veto remains, it is impossible to set out any “rule” which might govern the situation; the private and vigorous exchange of views between Sovereign and Prime Minister would be the best course. Indeed, in practice a Sovereign’s concerns about any legislation actually expressed in private might be of greater constitutional importance than the legal possibility of a royal veto. Further speculation is pointless. In law the veto remains. In practice it has not been used for more than 300 years, and perhaps it will never be resorted to again. And yet, who can say? One of the fascinations of constitutional law and practice is how it is affected by events, which in their nature are unforeseeable.