In the UK it sounds completely natural.
Definitely sounds affected in the US... either more polite than usual or distanced. Sometimes used when the speaker knows that's what the other person doesn't want. Shall in statements sounds very weird and is mostly limited to a subset of legal language.
dropped final or monosyllable 'r's",...turned the traditional flat "a-sound" into a broader sound as the good Prince typically was said to pronounce "half" like "hAHHf
Sounds like a language legend (like the lisping Spanish king).... dropping word-final and/or pre-consonantal rhotics is a phenomenon found across Europe in different languages, French, German, Danish, Catalan and even some types of very, very informal Spanish...
I know of no real world examples of one person having that kind of influence on pronunciation.
I can believe that people might cultivate features once they're aware of them... I get the idea there are a lot of closed language clubs in British society and local weirdness is maintained to keep outsiders.... out.
The American propensity is more often the opposite which is why GAE has such spread.