It's the accumulation of horrific detail that appalls and truly scares us - not just the putrefying bodies but the severing of civilization's entire network, modern man trapped in modernity's ashes.

Threads is most successful by its merciless refusal of sentimentality - every second is played for realism; this is a documentary of a nightmare, as we are taken, via a young unmarried couple, through a nuclear strike on Sheffield circa 1984, and beyond.

For all its grim hopelessness, Threads had a subtextual faith that people would understand all this before it was too late.

The War Game and The Day After are powerful enough, but Threads is the truly devastating watch.