No it's the remains of a giant Limpet, (patella giagantus) that roamed the earth before David Attenborough. At that time most of the UK except a small area around Harlow was under about 10 ft of water. The water suddenly receeded when the earth cracked to form the marianus trench and the said Limpet, the last of his kind, was left stranded, having lost his GPS whilst munching on some very fine eal weed just out side what now is Warminster.

I think!

Mr H