I remember seeing it at The London Pavilion, where most Hammer films seemed to be first shown at the time. Felix Aylmer played the lead with a Hammer regular the young Janina Faye also in it, I think, and it was pretty disturbing both as a subject and also a film.
Hammer weren't afraid to make subjects that were mostly shied away from, The Camp On Blood Island, Stranglers of Bombay, Terror of the Tongs etc. I suppose some would say they were made for sensational purposes, and they may well have been right. In those days they knew how to make films the public would watch.