Newton Abbot, Devon, UK
Successor to The Science Fiction Book Club (UK)
from June or July 1974 (expected) as ISFDB publisher of the monthly SFBC subscription series.
, a group of British book clubs, contained SFBC at the time, perhaps from 1966.
Concerning mid-1974 numbers 1087, 1088, 1089:
"An SFBC imprint of varying type on the dustjacket and book spine remains in various forms until Killer Pine
(May 1974), then with The Gold at Starbow's End
(June 1974) the SFBC logo is on the dustjacket only and the following book--Rendezvous with Rama
-- is identified only by the 'Readers Union' logo in all positions."
--annotation within the numbered list of The Books (/sfbc1.htm) at Greg Pickersgill's SFBC Archive (gostak.org.uk/sfbc)