The original question has been ignored. Unaccompanied singing is probably present at many of the above, but some are much better but as an infrequent festivalgoer I'll leave it to others to advise on that.

Also, Ireland is not in the UK (except for Ulster) & the question was about the UK not Ireland.

Am sure the originator of the thread is aware of the differing meanings of Britain, GB, UK, England etc & if not, I'd advise him/her to brush up on the sensibilities here!
I agree, Jim C, the BRITISH ISLES is not an acceptable term as they aren't all British.
Mind you, if that's so, surely the IRISH SEA should also be an unacceptable name?