Between 5-6mm wide. One looks like it has thicker ribs, but I think there are the same.
No interactions present.
The iSpot preferred name is Discus (Gonyodiscus) rotundatus. If you suggest this then you will see the other observations in the carousel.The snail that shows at the moment is not D. rotundatus (it is in Other Organisms not Invertebrates!)
I have the FSC Land Snail book and it only says D. rotundatus in it.
iSpot seems to follow some other list that has a lot of subgeneric names. A good check list with annotation is
Lat/Lng: 51.9194, -1.1484
OS grid ref: SP586248