It seems my fears for the Collared Dove family were well-founded. When I went out to check on the nest this morning I discovered it abandoned, lined with a sad heap of quills and soft down while a few feathers caught on the prickly leaves stirred gently in the breeze. In the pond below floated more silky feathers.
Though I could not believe that the eggs were untouched I was nonetheless slightly encouraged when Mr/s C-D came to sit on the nest later in the morning. S/he stayed for some hours and then moved off and waited for a long while, maybe expecting the other parent to return to brooding duties. Eventually s/he flew away and somehow the mournful calling of other doves in the vicinity seemed more pronounced.