Superficially similar to Lichina confinis and, despite its name, a more robust species. It also occupies a different littoral position in the upper tidal region with the barnacles

References: 
Smith, C.W. et al. editors (2009) The Lichens of Great Britain and Irelandd
Dobson, F.S. (2018) Lichens: an Illustrated Guide to the British and Irish Species
Ahti et al. editors (2012) Nordic Lichen Flora, Volume 3: Cyanolichens