A recurrent song throughout this series is "I Love To Love (But My Baby Loves To Dance)," by British disco artist Tina Charles (circa 1976).
Greater London Police is fictional and is likely used to avoid licensing disagreements with the real life Metropolitan Police Service.
Nicola Walker (Jackie 'Stevie' Stevenson), Adeel Akhtar (Ira King) and Josef Altin (Christopher Riley) also worked together in Unforgotten (2015), as DCI Cassie Stuart, Hassan Mahmoud and Tyler respectively.
Stellan Skarsgård saying of his role as DI River --- "There's not much research you can do because his condition doesn't really exist as we know it. It's a combination of problems, because he's not like people who hear voices -they're usually schizophrenic and lack empathy and he does not. But it doesn't make it less truthful. What attracted me to the script is that it didn't look like any other script I've ever read."
Actors Owen Teale and Josef Altin are both Game of Thrones (2011) alums; they played Alliser Thorne and Pypar, respectively.