According to Nigel and Jeanette's booklet;
"This short-lived firm existed from 1924 to 1966, having the second world war curtail their production within that period." They later became absorbed by Webb and Corbett, after a short while of having leased space from them.
If I say any more, I'll be copying out the whole lot of the info in the leaflet!
I have a footed jam dish, it was my Grandma's and so it has sentimental value for me. It too has a wealth of diamond shaped cuts all over it, but it has always fascinated me how the diamond shapes are all differing sizes and of different angles - they are all shaped around the rounded and flared shape of the bowl, the detail in the work is quite amazing. Complicated and difficult stuff.
Do the shapes and sizes of your diamonds all vary to accommodate the shape of the tumbler?