Small (c1.5") but I assume the colour of the fringe means it is a young Arion ater?
No interactions present.
I wouldn't like to say which species this might be, especially if it is not full-grown. Roy Anderson provided some info on the Arion slugs:
but they are tricky. I believe Roy is working on a new key to the group, which probably won't stop them being tricky but should make it easier to know exactly how tricky!
Entomologist and biological recorder
Moral of the story - stroke slugs, or leave them well alone ;)
Lat/Lng: 50.9637, -0.5647
OS grid ref: TQ008192