Just thought I'd add my thoughts to this thread - I agree with M in that it does look Nazeing like in the colour / bubbles etc. if so that would infer it is British made for the home market? Nazeing did do "mass production" of small glass items so they wouldn't have had to be too expensive.
I think it is to do with furniture - I have some old drawers on legs with castors on, which drive me mad because every time I open a drawer the whole thing moves - the dimensions of the inner square (4cm) would fit the legs - mine are about 3.5cm, to stop it moving about, and being made in glass would also (as has been said before) prevent the wood rotting from the wet mopping. The rounded shape also reminds me of those old sofa legs.
Perhaps we should be looking on the domestic front for research purposes! Country houses / domestic museums etc.
good luck with finding an answer,
Roberta