A member of the department has kindly given me this interpretation, qualified by the words "as far as I can discover ":
"'The physical progressing of building cases' means going at intervals to the sites of factories etc. whose building is sponsored by the department and otherwise approved to see how many bricks have been laid since the last visit. 'Physical' apparently here exemplifies a portmanteau usage (? syllepsis) and refers both to the flesh-and-blood presence of the inspector and to the material development of the edifice, neither of which is, however, mentioned. 'Progressing' I gather should have the accent on the first syllable and should be distinguished from progressing. It means recording or helping forward the progress rather than going forward. 'Cases' is the common term for units of work which consist of applying a given set of rules to a number of individual problems . . . 'should be confined to' means that only in the types of cases specified may an officer leave his desk to visit the site ".