I always assumed that (since it appeared at roughly the same time) it was the UK's variation on the same nuclear war theme as America's made-for-ABC-TV movie, The Day After, or the slightly later U.S. film, 'Testament'.

Like The War Game, 'Threads' focused on the fate of a single British city near a NATO air base, Sheffield, and two families: The upper-middle-class Becketts, whose daughter Ruth has been going with (and now pregnant by) the eldest son of the working-class Kemps. World War III leaves almost everyone dead — except for the pregnant Ruth, who gives birth in a stable during a thunderstorm, while a chained dog barks frantically.

Decades pass; the postwar population of the British Isles is lower than that of Midieval England. Ruth is now a white-haired crone in her forties, dying of cancer, blinded by cataracts caused by increased UV exposure. Her daughter, now twentysomething, is pregnant and delivers her child in a makeshift hospital; in the last scene, a midwife casually drops her newborn baby on her stomach, and the daughter gasps — the child was born with deformities, due to radiation-induced damage to her DNA (hence, the 'Threads' in the title).

This production was, to me, more affecting than its Hollywood cousins because its horror was more understated than cinematic, and so had higher production values — again, my opinion. I'm not sure why, but the scene of fire engines, silently deploying in the darkness to predetermined 'safe areas' outside Sheffield, the night before the war begins was chilling enough that it has always stayed with me as emblematic of impending disaster.