i would suggest that gaelic, irish and celtic become irish, scottish traditional, welsh traditional and english traditional.
irish: altan, calico, ewan mccoll, dervish
scots trad: poozies, battlefield band, capercaillie
welsh trad: fernhill, pyginclust
english: waterson/carthy, kathyn tickell, nancy kerr and james fagan, carthy/swarbrick
these come courtesy of the folk collection of my missus. you may have a hard time sourcing this stuff, if you want any more then pm or email me, she is a veritable mine of folk-information