Confidence: I'm as sure as I can be.
Notes: Just because it won't roll into a ball doesn't mean it isn't a ball-roller! Uropods at back end are flush with end of body so it has to be a Pill-Woodlouse. There is no other option. The gills are at the back end between the last legs. The 'lungs' can just be seen as white dots on the edge of these. As to species - a clear shot of the animal from above would help, but the raised scutellum (between antennae) suggests A. depressum, a very common species in SW Britain.