Have you googled "Kenart" jewelers Birmingham?
You immediately get lots of hits for their jewelry. Lovely stuff!
I just looked at a couple, and they were hallmarked Birmingham in 1949, 1944 1939, and ebay says they were there 1934 to 1952 (somebody must have done some research).
Trade directories are on a University of Leicester website
specialcollections.le.ac.uk › digital › collection
You could try a search there.
Some on Ancestry too - maybe these don't go as late as you'd need.