F & Bflat are quite OK for an English ( or Duet) concertina player, but a bit of a pig for an Anglo. Anahata is one of the few people I know who can play in such keys.
The 10-year-old fiddler - I wish we knew his name - said he had learnt the tunes from recordings. If he's at Whitby again this year,he'll probably be running a workshop.....