That still seems a bit stiff to me. but I dare say you know what you're talking about. My experience of meeting ambassadors is mostly at dinners or drinks parties outside the diplomatic circuit whey're they're guests just like everyone else, and if I addressed them as "Your Excellency" I'd be the only one doing so. I suppose Hiddy is meeting the ambassador in an official capacity.

Do you actually address a bishop these days with the formal style of "My Lord Bishop"? I've certainly met plenty of bishops and I think it would have sounded very odd. Simply "Bishop" or "Bishop Brown" seems normal, which is the social style. Some of the happy-clappy ones seem to want to be called "Bishop John" but I'm not holding with that nonsense. Similarly with Lords Temporal, whom I don't think I've once addrssed as "My Lord" in my life - it seems exclusively reserved for servants and for those addressing them in a formal capacity. The only place I've heard it a lot is walking around the House of Lords with a peer, when all the staff use the term constantly. Even with a Duke the formal address of "Your Grace" seems a bit forced. It's only with members of the royal family that I tend to stick to using the formal style (typically "Your Royal Highness" or "Your Majesty" as appopriate) - not that the opportunity arises often, and even then with minor royals at social occasions I think it's very optional.

Perhaps out in the colonies (in this case the Spanish colonies) things are still done the old way. Or perhaps it's just that official diplomatic events tend to stick to the old protocol more than anything else.