The tune Rigaud (Andy Serkis) often sings is called "Le Chevalier du Guet", also known as "Les compagnons de la Marjolaine".
Emma Pierson (Fanny Dorrit) & James Fleet (Frederick Dorrit) also worked on episode 2.4, Death in the Clinic (2013), of Death in Paradise (2011) as Anna Jones & Jeremy Tipping respectively.