Thanks for the information, the fellow I bought it from told me he bought it at a boot sale in Blighty, so I suspect it is British in origin, and come to think of it, I suspect that it is zinc rther than aluminum, I had not looked that close, but the weight is too much for aluminum (sometimes I am not the sharpest tool in the shed)
So I think it would be safe to assume that it is a movie prop, I hope it is inert, as I can not get the base plug out, oddly enough, this dummy grenade is banned in California, while it is still allowed to have inert grenades from WWII or earlier.
Best wishes
Gus