The main body is about 15mm across, and lives in my ferns but does turn up around the garden in dry dark places(inside planters etc)
No interactions present.
The appearence is S.bipunctata but if you are sure about the size ,it could be S.grossa,although the markings aren't quite right.
Lat/Lng: 50.838, -0.1178
OS grid ref: TQ326059