This overprint is from the firm Holloway's Pills and Ointment owned by Thomas Holloway (1800-1883).
The firm operated from
at the time the overprint was in use and later at both
113 Southwark Street,
533 Oxford Street,
The first two addresses are shown on the following pill box label (and no I did not deface the label, it was like that when I obtained it):
Royal Holloway College (now Royal Holloway University of London) was founded as a women's college by Thomas Holloway in 1879 and was opened by Queen Victoria in 1886.
186?. Unofficial overprint type 34 in blue.
PP111 1d rose-red (SG 40 or C10)
PP112 1d rose-red (SG 42 or C12)
PP113 1d rose-red (C13)