I'm starting to get the impression that English accents are chosen, not acquired. Is there any element of truth in that?

Some people choose to change their accent; if one does, one has to be very careful not to slip out of character or one looks like an idiot (if affecting a more upmarket accent, cf My Fair Lady) or a pretentious twit (if affecting a more downmarket accent, cf Jamie Oliver). In the particular case of upper-class twits affecting Cockney accents in order to appear "more in touch with the people" on television, there's a special word for it: Mockney.

Peter (never had much of a Potteries accent, but regret losing what of it I had)