In the HP universe, do Ты think that the British Sovereign is aware of the existence of the UK Wizarding Community ?

Hmm . . . Good Вопрос (and interesting concept of the wizard's being the subjects as much as the muggles). And I'm honestly not sure.

On the one hand, the King and Queen are still very powerful people (I've always been told that they're еще figure heads than actual leaders). I think they, just as much as the PM, would need to know if their country and people were in danger from a wizard. It would make sense that, like the PM, they would be told on a strict "need to know" basis. (Interesting that Lord Voldemort didn't go after the royal house. Even if they are just figure heads, he'd have the power and the symbol to back him when he took over...)

On the other hand, Voldemort didn't go after them (at least I'm assuming - the Order/Auror office was еще worried about the PM). The wizard's and witches may not really consider the King and Queen to be in any position of power. If that's the case, it would make sense that they would be kept in the dark.

I don't think they would. The Queen doesn't actually do anything much now, does she? She can't make decisions for England, that's the government's job. She's merely symbolic and there to keep the monarchists happy. Wizard's wouldn't bother to tell her, there is no reason to.