Hi Jonathan,
Welcome to the Forum.
Yes, the date that Walker & Hall registered the design was 12th September 1873. See:
British Registry Design Dates
My first thoughts were that the 'B' may be one of Walker & Hall's date letters, but that does not appear to be the case, and thus must be a quality indicator mark.
Do don't mention a size, but these pieces appear to be sugar crushers. In those days sugar was supplied in solid cones and lumps broken off and ground up prior to use.
Trev.