Chris â€” I've just read this topic for the first time and saw that your glasses also carry the official Weights and Measures Office Number of 542. Without this number the validity of the mark couldn't have been checked, the mark would therefore have been invalid, and the use of the glass as a measure would have been a serious offence.
What is nice about these numbers is that they can add interesting details, such as likely manufacturing glassworks locations. So I looked up 542 and, instead of the location of a Weights and Measures Office, my list has the entry "539â€“544 Unappropriated". :spls:
Fortunately the compiler of my list explains in the introduction. He explains that numbers described as "unappropriated" were issued mainly in the years following 1946, together with re-issuing numbers that had become obsolete by 1907. In 1946 the decision was made to allocate one number per inspector, rather than one number per office, increasing the numbers from 636 to about 1650. Also I wouldn't be at all surprised if new numbers were given to Weights and Measures Offices whose records had been destroyed during the war. I've never seen an "unappropriated" or re-issued number before, mine always seem to be along the lines of "323 Gateshead".
So, although we don't have a location, we do have a date. Your glasses were made in the years 1947 to 1952 inclusive. Lovely. It's not often possible to date glass so accurately.
Your local Weights and Measures Office should be able to tell you about 542, as they must have lists. Please let us know if you discover more.