Four of the regular cast, David Griffin, Judy Cornwell, Geoffrey Hughes and Clive Swift, had appeared in the original series of Doctor Who (1963) prior to the sitcom. Griffin appeared in a Jon Pertwee (The Third Doctor) era story in 1972, while Swift and Hughes both appeared opposite Colin Baker (The Sixth Doctor). Cornwell appeared opposite the Seventh and final Doctor in the original series, Sylvester McCoy. Swift is the only one to have appeared in the 21st century series as well, appearing in a David Tennant (The Tenth Doctor) episode.
In most episodes following the introduction of Emmet, he is frequently seen to stare out the side living room window of Elizabeth's house at the assorted goings-on next-door at Hyacinth's. However, all exterior shots of the house clearly show that there are no windows on that side of this room.
During the end credits, we see a table set for a posh dinner. When all credits have been shown, Hyacinth is shown rearranging a fork and a spoon and then putting a name plate on the table. As the camera zooms in on it, you can see that it reads Harold Snoad and the words "Produced & Directed by" appear above it (plus a copyright notice below it).