Phylum: Cynaobacteria   Family: Cyanothecaceae

Cyanothece major (Schröter) Komárek

This is nothing more than a much larger version of Cyanothece aeruginosa. Found in boggy ground amongst mosses and bryophytes. No doubt under-recorded but quite possibly rare

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles.