When I was very young, back in the early 60's, my grandmother used to take me to tea at the Ritz. I had to be on my absolute best behavior, as anything less would have completely unacceptable !
Its important that the sandwiches are cut into dainty little triangles, not bloody great slabs ! Afternoon Tea is a small meal, not meant to fill you up. Its purpose is to tide you over before the more formal dinner later in the evening. Small cakes, liked Iced Fancys are the norm, together with lots of tea in proper cups, and a proper tea pot ! If there are doilies involved, well all the better.
Of course standards have slipped terribly these days. You can probably have a "burger" and a coke in the Ritz now.