When was the Horizon special on the Standard Model?

Back in the late sixties or early seventies, the BBC broadcast a two-hour special episode of the science programme Horizon, explaining the Standard Model and the zoo of particles. It was extremely well-done. The presenter had gravitas, and the "graphics" were well-done and helpful.

It made quite an impression on me; I saw it exactly once, ~50 years ago, and I've never forgotten it.

I would like to know the broadcast date, and the name of the presenter. If there was some way I could see it, I'd be over the moon.

Horizon is still on TV. Modern Horizon programmes are pretty decent science programmes, but shallower than they were. The script is usually clickbaity, and the graphics and visuals they use are usually pretty random, like something a marketing consultant might dream up during a cigarette break - i.e. not likely to aid understanding.