Thank you Bernard

Unfortunately both pieces are in storage for the time being (which hopefully won't now be long with an imminent house move). I was unable to locate the Gammon rummer so couldn't physically compare the two. However, when I am able, I will take a picture of them both side by side for interest. This latter one didn't have the spiral on the base that the rummer had, and the contours or outline of the molding seen at the sides didn't strike me as being as pronounced as the rummer. Hope you know what I mean, I'm way out of my comfort zone when talking about this kind of glass
I'm still looking to see if I can find out what it actually is. The out-turned lip or rim, is perpendicular, so its impossible to use as a drinking glass. I thought it might be a jelly or dessert type glass but haven't seen anything like it yet. I just wonder if it might have had a lid of some kind, although there isn't a recess that it would fit in/on. It's an interesting piece and I can't wait to see them together.