I think that it may be a seaweed polyp, but honestly I have no idea.
No interactions present.
It's definitely a shark/ray eggcase of some sort so you might want to move this to "fish" using the edit tab at the top.
I agree with all the above remarks; I know these egg cases as Mermaids' Purses & you'll find a similar discussion about the particular species in an earlier Observation called "Mermaids Purse".
Lat/Lng: 50.718, -1.864
OS grid ref: SZ096909