It is an odd pontil. It's unfinished, but it's still rather flat, rough but not sharp. There is an area where glass not directly attached to the pontil appears to have sheared off.
The glass is transparent, not opaque. There are probably at least a half dozen candidates for the work just among English companies, but the opalescent work is unusual enough that I'm hoping someone will know it.
The uranium formula suggests a pre WWII origin. Although uranium has come back into use, I don't know of anybody doing work this size now with uranium.