Predators wild and domestic including humans may have scared her or attacked her. Or she may have left temporarily from being frightened and return to the area in the near future.

We are not sure your exact location in the U K. However you might contact the local RSPCA, Wendy Hermon at Swan Lifeline in Eton or the Swan Sanctuary to see if they had a swan rescue in your area or if they know about the nests. The Regal Swan