Before filming started on the pilot episode, Ann Burbrook was cast as Maggie Doyle and Lisa McCune as Roz Patterson. The two actresses swapped roles to avoid being typecast in the future.
John Wood's (Tom Croydon) favorite line from all 500 episodes of the series is "You shot Doherty's dog?", shouted by him to Constables Maggie Doyle and Wayne Patterson in the pilot episode.
Before her death in a car accident late in season one, Tom's first wife Nell Croydon was mentioned in almost every episode but was never seen. Afterwards, photographs of the character appeared clearly on Tom's desk showing her with their children (as toddlers) and eventually Nell would appear as a "vision" to Tom in season seven, the only time she was ever seen "in person" onscreen. This was of course a different actress used to provide Nell's voice in the episode of her death (in which her left eye is also briefly seen in a photograph Tom touches before her funeral). Behind the scenes, John Wood thought the idea of Nell being talked of but never seen was hilarious, and called her "non-existant Nell".
John Wood is the only cast member to have appeared in every single episode of the series, although fellow original cast member Julie Nihill also remained with the show for its entire run, but was used less and less in its later years, and did not appear in approximately thirty episodes.
During series production there were 16 episodes in various stages of production at any one time, from set to on location filming and script reads and rewrites. There was always 7 episodes ready to show and one ready to go in case of problems such as editing issues and station dropouts. .