No identification made yet.
No interactions present.
Yes, almost certainly a Sea Hare in resting/protective mode.
I suspect it might be Aplysia punctate as they have these curious marking, like excrescences.
Sea here http://thesaltyscavenger.blogspot.co.uk/2012/10/common-molluscs-of-rocky...
Lat/Lng: 54.1072, -4.7523
OS grid ref: SC201714