DVD Talk notes that it's not available here in the U.S. but can be had from UK outlets and says,
Nigel Kneale is a grand old talent of British television, although barely known in the United States. The Stone Tape is one of his legendary BBC telefilms, one often referred to in Science Fiction literature, but that nobody seems able to see.The Spinning Image says,
Approached from a purely supernatural perspective, The Stone Tape hits the back of the net on many occasions, with its aura of evil practically reaching out from the confines of a television screen to suck you into that infernal room where past events intrude on the present. The aural and visual manifestations are frightening enough, but [director] Sasdy's film reaches its peak when a solitary figure enters the time-slip vacuum, breaching the darkness to confront a silence that is deafening. It's a scary tripBritish Horror Films concludes:
this programme shows us just how perfectly tailored to television the horror genre can be, with a rattling good script and good performances. Think of other films when scientists try to study unexplained events; Amityville III, Hell House, etcetera, none of these has done scientists as well as this, here they ask deep search questions that are relevant to all unexplained events.