Confidence: I'm as sure as I can be.
Notes: This (1st photo)was a brighter orange than the photo shows; & totally lacking the smooth surface characteristic of H.panicea & also no volcano shaped oscules (the big excurrent holes); indeed virtually no oscules at all. Species-identification.org lists several shapes for Hymeniacidon perlevis, including cushion form, which this must be. Revisiting I found it had gone, but all over his area is littered or 'spattered' with the orange sponge which look like that to far right of photo beyond the 'cushion'; hence shot 242 taken at same spot. Shot 197 was a pinch of a "true" H. panicea compared with a Hym. perlevis ;the one smooth the other contorted. So I did the smell test (hadn't tried it before), & the true (yellow) H. panicea had a pungent smell of burnt gunpowder & the other indetectible.
It's abundance here also favour it being perlevis [3 sponges described as abundant,these 2 & cliona celata].
Not least I doubt wether H.panicea is orange, based on the colour description given in habitas
(which describes about 163 sponges of England & Ireland by Picton, Morrow & Soest) (surely the top authority?):-Green in etc,cream-yellow in shaded sites."Ash-grey,brown or (rarely) brownish-red when alive" (the quotes not mine).Finally none of the photos of H. panicea in any of the uk Identification sites I know are orange (24 photos in all,but some duplication). That's marlin.ac.uk,habitas,marine-species ie WoRMS,european-marine-life,species-identification, Wikipedia. See comment for further details.