Lecidella elaeochroma f. soralifera (Erichsen) D. Hawksw.
Seemingly less common than f. elaeochroma, noted for the production of powdery, creamy soredia (hence the name). The thallus has a greenish tinge
Smith et al. editors (2009) The Lichens of Great Britain and Ireland
Dobson (2018) Lichens: an Illustrated Guide to the British and Irish Species