I'm English and I agree with you about
Imogen,
Nigel,
Penelope,
Harry and
Beatrix. (
Nigel is a bit dated though)
Winston is a name (like
Reginald) which I have seen used more in the black / Jamaican community.
Edwin is really not popular here at all.
IMO nicknames as first names like
Millie and
Alfie are very 'British'