RECYCLING is the key activity of our day: instead of using up scarce resources for the first time, let us comb through the waste-paper basket to see what can be salvaged. Not only does it use up less stuff, it is also cheaper and, alas, employs fewer people.

The BBC has been around long enough to have — despite its eagerness to destroy recordings of early broadcasts — a back catalogue rich enough to make possible the compilation of any number of secondary programmes.

This has the advantage of adding that extra spice of nostalgia: for those of us old enough to have been around when it was first aired, the frisson of remembering what we then thought to be attractive ways of dressing, of cutting our hair, produces a suppression of critical faculties.

We are so seduced by those flickering, black-and-white days that we pay less attention to what is being said, and whether it adds up to a worthwhile argument. This view is not fair to the best examples of documentaries: to take a broad sweep of the past 50 years of factual broadcasting on any particular subject can be highly illuminating.

Women, Sex and Society: A Timewatch Guide (BBC4, Tuesday of last week) demonstrated both the strength and the pitfalls of the genre. Much of the material was fascinating, and well worth a second airing, but the cut-glass accent of the 1968 radical feminists interviewed undermined their professed eagerness to storm the bastions of power: they sounded securely within the strongholds of privilege rather than toiling among the masses.

It is good to be reminded of the revolution brought about by effective domestic technology, by the rise of the housewife, by women going out to work. A second strand is the liberation provided by effective contraception: the freedom from unwelcome abstinence, or constant child-bearing, or recourse to back-street abortion unimaginable to previous generations. The revolution is not yet complete: the internet now offers a platform for naked misogynistic hatred that would appal our grandparents.

There was a different kind of scissors-and-paste job in The Undiscovered Peter Cook (BBC4, Wednesday of last week). After the comedian’s untimely death, his widow, Lin, shut up his house (they had kept separate addresses), and only now, 21 years later, has she permitted a close friend, Victor Lewis-Smith, to sift through the tapes, cassettes, scripts, and home movies.

Overall, it was essentially sad and inconsequential, forcing the conclusion that we already have his best material — apart, that is, from a brilliant sketch with Peter Sellers playing a brain-damaged boxer-turned-abstract-artist, with Dudley Moore giving a brilliant turn as his Second, treating his attacks on the canvas as the rounds in a boxing match. Cook, by blank imperturbability, inexorably reduces his friends to helpless giggles. Eventually, it all came back to the Church of England.

Cook: “And who, exactly, is the picture of?”

Sellers: “Ain’t it obvious? It’s the Archbishop of Canterbury.”