Survivors (1975)

The 1975 BBC original, not the 2008 remake. Terry Nation's premise is brutal: a plague kills roughly 4,999 of every 5,000 people, and the handful left in rural England must work out how to grow food, make medicine and govern each other. What makes it hold up is how practical it gets. There are no zombies and few villains, just arguments about who milks the cow and whether to share the seed corn. Series one is the tensest, with the first episode a genuinely chilling hour of TV; later series settle into slower community drama across 38 episodes in all.