Saturday evening's By The People - The Election of Barack Obama helpfully illustrated some timeless truths about the art of documentary film-making. Its co-authors, Amy Rice and Alicia Sams, had spent two years enjoying priceless backstage access to Barack Obama's campaign for the presidency, first as he saw off Hillary Clinton for the Democratic nomination and then during the Presidential campaign itself.

On Have I Got News for You, the world viewed through Paul Merton’s eyes is not quite as others see it. He makes the random connections of the lateral thinker, thinks jaggedly round corners, and competes manically to have the last word, the last laugh. He also likes you to know that he knows stuff. Last night Paul Merton went to Germany to make a documentary. He’d never been before. You rather fancied that Germany viewed through the Mertonian prism might come up looking a little different, perhaps even a little funnier. But no, I didn't laugh once.

If Gordon Brown had slipped and fallen on the ice this weekend you could have expected at least a dozen conspiracy theories to have emerged on the internet. Why was David Miliband spotted studying a weather map the night before? Why had the PM’s aides suggested that particular pavement? And who controls the gritting lorries anyway? The worldwide web is many things, and one of them is this festering, bottomless pit of paranoid conjecture – rich picking for a tough-minded series like BBC Two’s The Conspiracy Files, whose latest chosen subject was Osama Bin Laden.

For Horizon's fascinating investigation into the ancestral relationship between man and dog, a record-breaking number of illustrious boffins had been compressed into 60 minutes of television. We met Dr Anna Kukekova from Cornell University, who has been conducting research into which gene makes silver foxes (dogs by any other name) either tame or wild.

Perception was everything last night in Garfield Kennedy’s fascinating if, at times, frustrating documentary, The Trials of Amanda Knox. Was the American student who was convicted last month of murdering her British flatmate in Perugia, Meredith Kercher, a scheming hussy into (very) extreme sex games, or just an averagely adventurous twentysomething turned into a scapegoat by an Italian judiciary that had already convinced itself of her guilt? Kennedy’s film considered the evidence, and it also detailed the concomitant trial by the media - and there, to a degree, is a problem. Because this documentary is also “the media”, and Knox’s case (appeal pending) is not closed. Somewhat misleadingly, it could be argued, the film was screening in More4’s True Stories slot. But was this only the partial truth, with some added special pleading?

Television doesn’t do eroticism at all well. Perhaps, rather like a truly horrifying horror film being unwatchable, a properly erotic drama would never pass TV’s internal censors. Dennis Potter tried it with his 1989 love letter to Gina Bellman, Blackeyes, but ended up dubbed “Dirty Den” for his troubles. And what is erotic anyway – just a glimpse of stocking, or the full-on and (for me, anyway) embarrassing sight of Billie Piper in fishnets and suspender belt? It's a question of taste, I guess.

Saving the planet from ecological disaster is all very laudable, but be careful what you wish for. In this two-part Anglo-Canadian production of John Wyndham's 1951 sci-fi novel, the voracious man-eating plants called triffids had been artificially cultivated as a fuel source, so successfully that triffid oil had enabled the world to wean itself off fossil fuels and thus curtail global warming. The story didn’t bother itself with those pesky climate change deniers.

There was something very postmodern about the resumption of Quentin Crisp’s story. To recap, in case you missed episode one back in 1975, The Naked Civil Servant has been turned into a successful television drama, and its subject into a celebrity.

The end of the South Bank Show? Surely some mistake. But there was Melvyn, looking into the camera with a resigned air, telling us that this film about the Royal Shakespeare Company (“possibly the greatest theatre company in the world”) was indeed the end of the line, give or take the occasional retrospective special.