If the late Labour leader had lived into the era of Who Do You Think You Are? his episode would have revealed a story to beat them all.
Neal Ascherson tells it in his book Stone Voices: The Search for Scotland:
John Smith’s father was the head teacher at Ardrishaig, a little town on Loch Fyne where the Glasgow mailboats used to end their run. But the family’s roots lay a few miles further south, in a forgotten settlement called Allt Beithe in the hills beyond Tarbert. His cousin John Smith of Glendarroch has told the story of Allt Beithe’s terrible end, and of the providence which allowed them both to be born.
In 1845, a year before the potato blight, the cholera plague reached Argyll. Perhaps a dozen people lived in the settlement then: it could be reached only over a long, rough track, and it was some days before friends in Tarbert noticed that nobody from Allt Beithe had been seen in the town for a while.
A rescue party set out and went first to the hamlet of Baldarroch, where they found only the dead lying in their houses. Climbing on, they reached Allt Beithe. They “found everyone dead or dying except for a baby, Archibald Leitch, a little boy of two".
He was carried back to Tarbert and brought up by relatives, and in time grew up to become a boat-builder and the great-grandfather of both John Smiths.