Caloplaca phlogina. This species was originally lumped with the Caloplaca citrina aggregate, and most material with this sort of sorediate thallus on trees, which isn't very frequent belongs to this species. It is the paler yellow fruited lichen with the greenish yellow soredate thallus in the photo. The other is Caloplaca ulcerosa, and the photograph was taken on the same ash tree in Parham Park, West Sussex.