Thallus death due to Xanthoriicola physciae?
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 wonder if it is something else, as you know I am not a lichen expert so could be talking rubbish here but in that close-up in http://www.ispot.org.uk/node/241410 you can see the black covering of spores which looks a bit rough whereas your blackening looks rather smooth.
Lat/Lng: 52.6, -9.1
OS grid ref: SE2225