This is not coral at all, but broken pieces of calcified red seaweed known as maerl. For more information about maerl, see the UK Marine SACs project website.
top: Clausinella fasciata (Banded Venus), Trivia monacha (Spotted cowrie), Hinia incrassata (Thick-lipped Dog Whelk), Gari tellinella (Sunset Shell).
centre: Gibbula opercularis (Flat Top Shell), Gibbula cineraria (Grey Top Shell), Tectura virginea (White tortoiseshell limpet).
bottom: Parvicardium exiguum (Little cockle), Lucinoma borealis (Northern Lucine), Aequipecten opercularis (Queen Scallop).
Below are some larger shells, clockwise: Gari depressa (Large Sunset Shell), a piece of Maerl, Dosinia exoleta (Rayed Artemis), Venerupis senegalensis (Pullet Carpet Shell), Circomphalus casina, Mya truncata (Blunt Gaper).
For more about seashells, see our UK Seashells website.