Doomwatch (partially lost BBC sci-fi TV series; 1970-1972)
Doomwatch was a BBC science fiction show created by Gerry Davis and Kit Pedler, better known for creating the Cybermen from Doctor Who. They had an interest in science changing and endangering human life, which leads them to create Doomwatch. It ran for 3 series of 13 episodes each, apart from the final series which was 12 episodes long. This totaled 38 episodes.
Doomwatch (or more properly "Department for the Observation and Measurement of Scientific Work") was an agency dedicated to protecting the public from unprincipled scientific work. Under the leadership of Dr. Spencer Quist, they tackled threats to the human race, many based on real science.
As was common at the time, the BBC junked many of the master tapes. Though many were returned from Canada, or exist as telerecordings, 14 episodes remain lost. Ironically, one of the surviving episodes is the unbroadcast "Sex and Violence". The 14 lost episodes include 5 from the first series, and 9 from the final series, with Series 2 remaining complete.
The surviving episodes (including "Sex and Violence") are available on a DVD released in 2016.