I think re the Irish and Scottish music, it often conforms to 1 or 2 sharps, eg A mix?

Fair enough if that's the case - not particularly my area of interest/expertise.

If it's a song you're dealing with, then key is paramount, and the most important thing is getting the key that suits your voice, regardless of the written key.

At the session on Sunday someone started singing unaccompanied, and was doing very well and fine thank you until some eejit on a silver flute tried to join in with the tune, found the original singer was on a tonic of somewhere between D and C# ... and played along increasingly loudly until the singer was pretty much forced to pitch-shift up to D. Personally I'd have deliberately gone flatter and/or changed the song words to tell her to butt out, but there ya go ...