The final 13 episodes, combined series 4 and 5, were actually shot at various locations within the Republic of Ireland, mostly around the Dublin-Wicklow area, some with none to major digital set dressing enhancement. The city wall map in the office, in Series 4 and 5, is actually Dublin City, turned upside down.
Wellington Zoo scenes were filmed at London Zoo and Whipsnade Zoo.
Lucy Brown, James Murray, Andrew Lee Potts, Juliet Aubrey, Ciarán McMenamin, Laila Rouass, and Anton Lesser have also appeared in Midsomer Murders (1997).
Ben Miller (James Lester), Hannah Spearritt (Abby Maitland), and James Murray (Stephen Hart) all appeared in Episode 6 (2013).
Two of the main characters are named Sarah: Sarah Page and Abby (Sarah) Maitland.