Possible fungus-induced galls (to 4mm) on Acarospora fuscata (C+ red) growing on vertical, well-lit gritstone.
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.
Polycoccum is a genus of pyrenocarpous fungi in which the perithecia are individual and usually immersed in the lichen thallus. A couple form galls, but apparently not P. microstictum. I don't think it can be this.
I don't currently have any other ideas though.
A quick squash didn't seem to offer much more than algal cells but I will look again, and if all else fails, think about troubling a referee (Mark Seaward if I follow the request to use a local contact).
Thanks again! A lichenicolous lichen didn't occur to me. I will test when I get back home.
Edit: No reactions (C-, K-), despite buying fresh bleach and testing it on Ochrolechia parella, and checking the K against Pertusaria pseudocorallina. Perhaps because it is immature. The chlorobiont cells are around 7.5-12.5μm. R. furvella still seems the best bet.
Lat/Lng: 53.1616097, -1.6373406
OS grid ref: SK243627