Royal protocol
Apparently this is the correct procedure for meeting said bigwigs:
If [the royal in question] approaches you, bow/curtsey, shake hands if offered, let him speak first, and the first time you speak address him as "Your Royal Highness" and after that as "Sir"
This is from our official instructions. Other gems include an exhortation not to use the toilets (presumably we don't want to offend the royal nose).
Fortunately, I have the day off.