Every year there are a couple of Proms that have a haphazard look about them, as if a fire had suddenly broken out in the BBC archives, and the programming committee grabbed whatever came to hand – a piano quartet, a couple of choral odes and a concerto for mandolin – and made for freedom. Though there had evidently once been a clear architecture to Sunday’s concert by the BBC Symphony Chorus and friends, in practice things were somewhat confused; endless personnel shiftings and a stuffed-to-bursting programme blunted the impact of music which demanded altogether simpler treatment.