This underprint is thought to be from the firm Mander Brother's. They were Varnish and Paint Manufacturers of Wolverhampton (as indicated by the “905” cancel on the only recorded example):
Mander Brother's also had offices in London with a
business directory entry from 1865 of:
Mander Brothers, varnish manufacturers, 363 Oxford st.
1868. Unofficial underprint type 8 (over the gum) in blue.