The "lift voice" heard during the theme song played in each episode is that of Stephanie Gathercole who plays Mr. Rumbold's secretary in the earliest episodes.
Mrs. Slocombe. I suggest you take your underwear down at once.
Mr. Lucas: Same goes for Miss Brahms.
Throughout the series, the entire staff of the floor takes breaks together. That would mean that the entire floor would be closed due to lack of employees during break times. Indeed, one episode specifically deals with this problem. Mr. Grace feels that they are losing too much business during this hour, and pushes the lunch break back to later in the afternoon, leading the staff to hit the roof.
The closing credits listed the actors' names but not the corresponding names of the characters that they played.