Sue, thanks for popping this up to the top. I never even noticed it before. Apolgies to izzwizz (neat name :lol: ) and I hope someone will be able to give you a positive ID.
I am aware of glass shells that are more like scooped dishes on a flat base. Westmoreland, for example, made them. But this one doesn't seem to be dish, more of an upright, sculptural form. Have Alum Bay made this sort of thing at all? I have seen smaller iridised shells, that I believe were made by them.
Hopefully someone will be able to give you better info than I have, izzwizz.