For an hour or two this week, I’ve been in the company of people whose lives I’ve seen unfold, almost from the beginning, almost to the end. They are people whom, with one exception, I’ve never met. And yet I’ve shared in their triumphs and disappointments for decades.

They are the group who, in 1964, when they were seven years old, were the subjects of what was initially a single, 40-minute ITV documentary, but which flowered into a work that is quite magical. Returning to those same boys and girls every seven years, watching as they turned first into shy and awkward teenagers, then into husbands and wives, then into parents and grandparents, the 7 Up series has become a document of our times – but also something larger and far more revealing. This week the broadcaster aired what it says will be the final chapter: the seven-year-olds are now 70.

The original aim of the show, made under the World in Action banner, was sociological and transparently political. It wanted to expose the entrenched nature of the British class system. And so it watched a trio of pre-prep school boys singing verses in Latin, contrasting them with the cheeky East End kids living just a few miles and a world away. While the posh trio could name, even then, the specific Oxbridge colleges their parents had in mind for them, Paul, raised in a children’s home, asked: “What does university mean?”

Sure enough, we have seen how those born into money keep it, while those with less have less – though what the programme missed was the huge and expanding group in between. By focusing either on foxhunting John at one end or cabbie Tony at the other, it largely left out what would turn out to be the story of these decades, namely the sprawling growth of the middle class.

Indeed, it’s the programme’s early assumptions that often turn out to illuminate most sharply how much society has changed. In 1964, the researchers only thought to include one child who wasn’t white: Symon. In a later........

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