I agree that it's up to the club to decide its own policy and how rigidly it adheres to it. I think the latter part is important.

I'm in a band that plays mainly English traditional music. To us, the "mainly" is important. We do a couple of songs that are not English and a couple that are not traditional, including at least 2 that are neither English nor traditional. Personally, I'd be uneasy about not being able to sing a particular song that I liked because its origins lay in the "wrong" country or the wrong century. Some ensembles, however, do restrict themselves to a particular region or era. Good for them! If artistes can do this, why not clubs?

We won't be asking any jazz or blues clubs for gigs, although we would be happy to play our mainly English music anywhere in the world if invited to do so (and it's viable!).

dj