Found in an old oak wood in Derby.
No interactions present.
This is a marble gall caused by Andricus kollari in the Hymenoptera: Cynapidae (it says in the book I have). The oak apple gall is larger lumpier and initially quite soft.
That's what I hoped to find out.
Lat/Lng: 52.947, -1.4322
OS grid ref: SK382389
This site is thought to be an ancient wood