In earlier days, builders had their own supplies of stop tap covers and inspection chamber covers, usually sourced from local foundries. It's still possible to see many examples locally with the name of the builder cast in the surface cover. There are a few in Craig y Don with "W. Dobinson & Son" on them. Another local builder and funeral undertaker who was based in Builder Street (!).
Bri - I think there may have been two separate Gorst firms, Eldon R Gorst and O E Gorst & Sons.
Another couple which come to mind from the 70s:
Dodwell Builders
McNeill & Co