Surely there's no such thing as "traditional instruments" in Cotswold, in the sense that 100 or 200 years ago dance musicians didn't deliberately restrict themselves to certain instruments and avoided others. No doubt, like the parish bands that played in the west gallery (they must have been the same people playing on the village green on Saturday and in church on Sunday) they used whatever they had. If someone had a trombone or banjo I'm sure they would have been in there. To my mind, once you decide that some instruments are "authentic" while others aren't, you are doing historical re-enactment and to be consistent dancers and musicians should perhaps be in appropriate costume.