Acting for Two: Monica Dolan as Mave and Meg Carter in series 2, episode 3.
All There in the Manual: Sister Bernadette's first name is revealed in 2x08, but her pre-convent surname of "Mannion" was only revealed in the credits list.
Anachronism Stew: Largely averted, but there's a particularly glaring example with the Establishing Shot of The London Hospital, which shows the name "The Royal London Hospital"—an appellation it didn't get until the Queen's visit in 1980.
Edited for Syndication: PBS, as is its wont, cut scenes for the American release. Fans, as is their wont, were enraged.
Stephen McGann, who plays Dr Turner, has been fondly nicknamed by his fanbase "the Human Disaster" (for his questionable sartorial choices and general adorkableness). This nickname is as official as it gets; to the consternation of the whole fandom, it appeared in the Radio Times.
Similarly to the above, Laura Main has been nicknamed "the Pocket Soprano" because she is tiny and a soprano.
"DTE", or "Dr Turner Effect", refers to Stephen McGann — and his character, Dr Turner — making women everywhere swoon. Any photograph in which he looks particularly attractive will be labeled with "DTE".
Sharon Small (Nora Harding, episode 2x05) previously played DS Barbara Havers on The Inspector Lynley Mysteries. Jenny Agutter (Sister Julienne) made a guest appearance in episode 3x03 of that programme, A Cry for Justice, playing Jemma Sanderson.
Real-Life Relative: Screenwriter/show creator Heidi Thomas is married to Stephen McGann, who plays Dr Turner. (McGann good-naturedly grumped that just because he's married to the head honcho doesn't mean he gets a preview of what's coming; he had to wait to find out whether Sister Bernadette and his character were going to end up together until he got his script. For the record, they did.)
Reality Subtext: Episode 3x01 dealt with cystic fibrosis because Jenny Agutter lost two infant siblings to the disease, and her niece has it as well; she has since focused most of her charity work on finding a cure.
Also, Sister Monica Joan's struggles with dementia are very much coloured by the fact that Judy Parfitt's real-life husband died of Alzheimer's, which obviously shapes her performance.
Shipper on Deck: Stephen McGann and Laura Main ship their characters almost as desperately as the fans do. Possibly more.
Star-Making Role: For Jessica Raine, Helen George, Bryony Hannah, and Laura Main.