https://digital.library.lse.ac.uk/Documents/Detail/report-on-the-census-of-production-for-1987.-pa241-structural-clay-products/454675
Report on the Census of Production for 1987. PA241 Structural clay products - LSE Digital Library
https://digital.library.lse.ac.uk/Documents/Detail/report-on-the-census-of-production-for-1992.-pa241-structural-clay-products/459863
Report on the Census of Production for 1992. PA241 Structural clay products - LSE Digital Library