From the links suggested above, Sproatly Smith are about as twee as it gets; good players on their instruments, unusual arrangements, but breathy little-girl vocals and no bass end. Telling the Bees have a much gutsier sound, albeit rather pointless lyrics and reined-in delivery. (They look vaguely familiar, I think I must have met them somewhere).

Boxcar Aldous Huxley (also on the Weirdlore site) are another Telling the Bees - terrific instrumentals but the singing is a bit dull.

I guess what I'm looking for is a sort of folk Meredith Monk.