https://digital.library.lse.ac.uk/Documents/Detail/report-on-the-census-of-production-for-1973.-pa399.5-drop-forgings-etc/433264
Report on the Census of Production for 1973. PA399.5 Drop forgings; etc - LSE Digital Library
https://digital.library.lse.ac.uk/Documents/Detail/report-on-the-census-of-production-for-1978.-pa399.6-metal-hollow-ware/441324
Report on the Census of Production for 1978. PA399.6 Metal hollow ware - LSE Digital Library