Foliose lichen growing on dry stane dyke.
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
I think you are correct suggesting it is Parmelia saxatilis. The lobes have the network pattern of pseudocyphellae and the lichen has lots of isidia. Perhaps check other images for comparison by entering 'Parmelia saxatilis' in the 'Search iSpot' panel and then add a revised identification if you think it is likely to be Parmelia saxatilis.
Lat/Lng: 55.4732, -3.2022
OS grid ref: NT241205