The origin of this underprint is unknown at the present time but one of the most likely users appears to be the firm Harry Hall.
They were Tailors advertising themselves as The Coats & Breeches Specialist trading from two locations in London:
1869. Unofficial underprint type 27 (over the gum) in black.
Note. The above is my numbering as this stamp is currently unlisted by Stanley Gibbons.
Plates 13 and 14 have been found unused.
A single perfin has been identified as belonging to this firm. I do not have an illustration of the perfin but it is referenced in Tomkins as:
See the Philatelic Links and References page for more information on Perfins.