how do you define proficient singing,
for example someone can be perfectly in tune,but give a mechanical performance.
another performer may be slightly nervous [perhaps its their first or second time singing] and go slightly out of tune, yet interpret the song better than the aforementioned singer,
in the end its up to the organiser to decide who sings or not, a new singer should be followed by someone the organiser knows is reliable[to bring the evening up ].
the mc should think carefully about contrast,if he knows his singers well,he can do this. so in the end proficient singing[ however we define this]is in the hands of the mc.
another important point,[if the guest is a concertina player accompanist]dont put another concertinist, immediately before the guest [THINK CONTRAST].Dick Miles