I'm sorry to get in this thread without any real knowledge on the subject, but constitucional politics interest me so it was a fine read.
Comparing to Portugal, we have a President that - unlike, for example, what happens in the USA - is not the head of government and so, if all things work peacefully, is no more than a ceremonial figure also.
However, he holds a few important powers, he can veto laws both from the Parliament and the Government (but a more substancial majority in Parliament can approve them afterwards and he must sign them then), he can dissolve the Parliament whenever he wants, he appoints and dismisses (not sure if this is the right word) the Prime Minister but he must do the appointment according to the results of the elections, so not much power there. And to "dismiss" a PM is something he only can do in case of constitucional crisis.
However, and apart from the "veto" power, very rarely used, he really only has the "A-Bomb" (in political terms) that is dissolving the Parliament whenever he wants.
Now, about the Queen discussed in this thread, I read Famine's interpretation of their "powers" as being mere formalities and that all things she can do are advised by the PM (in Famine's interpretation this equals being "told" by the PM to do it).
My simple question is. What if she doesn't take the "advice"? I don't care if it is unlikely, let's assume this happens. What happens then?
And the question is put from a "constitucional" point of view. So, if the reply is "the monarchy is finished then" it doesn't really answer my question because in that case we would be talking about a constitucional change.