All marked swans on open water (Except the Thames) belong to the monarch - They are a protected species but I can image the late queen gnawing through one !
It's unmarked mute swans, and someone would be in trouble if they hunted, caught or ate a swan even the monarch! But yes, I wonder whether she was served a swan in a country that holds such values.
Well researched !
People are odd in this country, when it comes to animals and birds we are very protective
When It comes to people ... not quite so much ! :~)