Flat red seaweed. Part of large expanse of red seaweed (of various kinds) washed up on beach.
No interactions present.
Grateloupia filicina Description from algaebase http://www.algaebase.org/search/species/detail/?species_id=131
"Compressed, tufted, dark purplish brown fronds, to 120 mm high, main axis 1-4 mm broad. Once or twice pinnate, axes and branchlets tapered at base and apex."
I cannot see if the branchlets are tapered at base and apex; any chance that you still have the specimen that could be teased out a bit? Or perhaps you can see ithis on your original photo?
Lat/Lng: 50.5, -2.5
OS grid ref: SY6777