Type 8

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):

"905"
Wolverhampton

Mander Brother's also had offices in London with a business directory entry from 1865 of:
 

Mander Brothers, varnish manufacturers, 363 Oxford st. W.

 

1868. Unofficial underprint type 8 (over the gum) in blue.

PP18 1d lake-red (SG 43 or G1)
Plate 119