Small grey bird with pale underside near its nest hole which was made smaller with a ring of mud, high up in an oak.
No interactions present.
Nuthatches ues either a natural hole in a tree or woodpecker holes (or nestboxes on occasion), they don't excavate them themselves. They may use holes with large and irregular entrances, but all are plastered with mud to reduce the entrance to a tight fit for the nuthatch. I have seen a hole almost the size of a postcard, filled with mud, except for the entrance.
Lat/Lng: 52.7, 0.9
OS grid ref: TF9918