Confidence: I'm as sure as I can be.
Notes: It's common & widespread (sublittoral)& commonly found on the strandline.
britishbryozoans.myspecies lists about 9 species of Alcyonidium but many are flat sheets, & only Alcyonidium hirsutum & Alcyonidium condylocinereum seem to have similar shapes; but A. hirsutum (unlike diaphanum) is matt when out of water & A.c.is grey (& also rarely recorded).(Hayward etc's 1996 collins seashore of brit & eur. on P.336 says "it probably consists of 3 or more, presently unrecognized species").NB dont try to add this to your seashore collection as it biodegrades to a smudge.