Wheel Nut:
I think you are on the right track with that. Leys Malleable Castings was taken over by Georg Fischer in Lincoln. I used to go to the North Hykeham site.Sir Francis Ley built his foundry on the original site of the RAMS when it was the baseball ground. There were several foundries in Derby, the largest of these being Leys Malleable Castings and Qualcast.
Sir Francis Ley business park is still there at the top of Osmaston Road
Qualcast had a works in Smethwick as well Malc. Originally it was Birmid then Birmid Qualcast.Their chimney chucked some good old s*** out along with a load of others in that area. 
I like the " Sir Nigel Gresley " nameplate. Seen that loco regular in my youth as a trainspotter…then totty took over