I am one of the few people in Canada who was trained to direct such television studio drama (by the New Zealand Broadcasting Corporation around the time when Upstairs Downstairs was being made). Each scene, and sometimes the whole show, is shot as it happens as if it were on stage. The actors must know their lines for the whole scene, and more, not just for each shot. As the director calls, images from each of the several studio cameras are selected as each scene unfolds. Cameras move with the action. Actors, crew and cameras moving with concentrated, synchronized purpose is something to see. It's exhilarating to be involved in such a thing.
There is an energy in such drama which is unique to television. As Alfred Shaughnessy, script editor and writer of several Upstairs Downstairs episodes wrote in the writers' guidelines:
Television is electronic theatre and not second rate film.Exactly. Good television studio drama, that is.