A big fat, shiny black slug.
No interactions present.
It could well be Arion ater (and the black foot fringe does fit with that), but the other Arion slugs have black forms as well. Also, it may still be a juvenile in May. I wouldn't be confident of deciding on the species for this one.
Entomologist and biological recorder
Lat/Lng: 51.2, -3.8
OS grid ref: SS8047