The dinner conversation about the limits of Holmes' knowledge (literature, astronomy, politics, etc) is taken from a list made by Dr. Watson in Sir Arthur Conan Doyle's first Holmes story, 'A Study in Scarlet.'
Neve McIntosh revealed in a 2002 interview that playing Beryl Stapleton brought back painful memories of being physically and mentally abused as an 18-year-old by her first boyfriend.
Ian Hart reprised his role as Dr. John Watson in Sherlock Holmes and the Case of the Silk Stocking (2004). He also played Sir Arthur Conan Doyle in Finding Neverland (2004).
Holmes' use of cocaine while on a case is non-canonical---in Sir Arthur Conan Doyle's stories, Holmes used cocaine only he was bored due to inactivity.
Richard Roxburgh also played Holmes' arch nemesis, Professor Moriarty, in The League of Extraordinary Gentlemen (2003).