I'm American, but we do have one fully British alter with perfect "accent" that people seem to love to hear. She's quite proper. Being the Narrator (for when no one else in the system can speak) perhaps she came by way of Narrator in Christopher Robin and Pooh. I think there are other factors; my aunt is from London (even tho we never liked her), and once when I was having heat stroke at Disneyworld, a woman from Nottingham with the most lovely lilted speech, stopped my father and directed his attentions to us and how to care for us - she even waited with us while he went for ice water. I was just 18. I wouldn't even hear of the word "Dissociation" for another 8 years. We often think of her and her kindness, and how she pronounced "Notting-um" instead of "Notting ham" like in Disney's Robin Hood.