The tea room guest book contains the names Tom Coates, Lily O'Hara, and Alex Moat. They are the standby art director, key floor runner, and script supervisor, respectively.
When Winter and Barnaby were reviewing the flight path of the drone deliveries, he mentions if the drone flew "as the crow flies." This was originally part of maritime operations. Crows were kept in cages and released from the crows nest as they would fly directly towards land. It later came to mean taking the most direct/shortest distance (or path) between two locations.
Both Abigail Cruttenden (Nell Fryer) and Claire Skinner (Kitty Oswood) play sitcom wives to Hugh Dennis in Not Going Out (2006) and Outnumbered (2007), respectively.
Samuel West (James Oswood) appeared in Jane Austen's Persuasion (1995) with Ciarán Hinds and Amanda Root.
The windmill seen in the background early on is the same windmill used as Caractacus Potts' home in Chitty Chitty Bang Bang.