W. H. Smith & Son are the Newsagents, Stationers and Booksellers that still exist today.
Their head office at the time of the underprints was:
1867. Official underprint type 55 (under the gum) in red or blue (on 2d).
a) Vertical underprint, reading upwards
b) Vertical underprint, reading downwards
Essays of a sans-serif W. H. Smith underprint on the 1867 1s., Plate 4, are known.
Other Essays in various colours are known on the 1d. Plate 95 (overprints as well as underprints on the same stamp). These differ from the official underprints in that the address is omitted.