Continuity mistake: When the milkman picks up the empty bottle, the note is flush with the top of the bottle, but when he stands up it it is sticking halfway out.
What to Wear When Yachting - S3-E7
Revealing mistake: At the beginning of the episode, when the TV repairman is at the door, you can see that the background behind him is a studio wall - not the front yard we normally see on that side of the house. This effect also appears in many other episodes.
Answer: I have asked myself the same question for a long time. It is Rosina-Queen's fine bone china, pattern "Olde England." It's the china that appears most of the time in the series. The Royal Worchester double-glazed Avignon (for candle light suppers) is really Royal Doulton Avignon, pattern "The Moselle Collection." And the Royal Doulton with the hand painted periwinkles is in reality of course Royal Doulton Colclough, pattern "Braganza."