It's a fossil coral. We're all more familiar with colonial coral, such as form coral reefs today, but in the past and today, many corals are solitary. The soft parts of the animal, with tentacles looking a bit like an anemone, would have lived in the "cup" on the left of this picture. It would have lived on the sea bed and filtered food from the sea water. It is probably Carboniferous in age and so roughly 300 million years old.
I'll see if any of our coral experts can tell you more about the species and age.
Thankyou for your speedy reply, I am looking forwards to further information about my find.
hi its looks like the solitary horn coral aulophyllum or dibnophyllum
age is probabally carboniferous