Hi Hel (and welcome)!
No longer a mystery I´m hoping...

Looks like it´s been made by Ingridglas, from their ´Lord Nelson´ range - guestimated somewhere
around the 70´s. Here´s an example on ebay:
click me.
Thanks to Pamela for pointing my nose here again! I read your post some time ago, when I was in a complete hurry and
meant to reply later. Well, better late than never...
Do the measurements fit with your piece? Does it have a ground and polished top rim (like I´d expect from an IngridGlas piece)?
Regards,
Dirk