Last Night’s Viewing: Secret Eaters, Channel 4 Felicity Kendal's Indian Shakespeare Quest, BBC2

According to Anna Richardson, "we each make about 200 eating decisions a day". Judging from the ballooning of the national waistline, pretty much all of those decisions are "Oh go on then. I shouldn't but I will".

We kid ourselves that something else is happening, naturally, convinced that we have somehow transcended the essential laws of the universe by creating matter out of thin air. "I don't feel I do eat too much," said Jill, her face a mask of bafflement, "Maybe sometimes I don't eat enough." Her brother Stuart, who's gone from nine stone to 16 "knows for a fact" that he takes in less than the recommended daily calories for a man. Both of them apparently sincerely believed that their inability to lose weight was "a mystery". The question for Secret Eaters, Channel 4's latest deployment of all-points surveillance, was whether they were exceptionally stupid or simply representatively self-deceiving.

The method is straightforward. With their acquiescence, the chubby guinea pigs have their houses fitted with cameras to record every surreptitious nibble. Unbeknown to them, they are also tracked when they're out of the house by two private detectives who take long-lens photographs of them sneaking in a quick prawn sandwich here and there. After a while, the evidence is amassed in what Anna Richardson grandly calls the Incident Room, stained takeaway boxes tagged as Exhibit F and a congealing smorgasbord of everything they've eaten and drunk over the preceding days. The guinea pigs swing round and make OMG faces at the scale of their invisible consumption.

The mystery, it turns out, isn't mysterious at all. Jill's sense that she "occasionally" treats herself to a snack turns out to be a steady conveyor belt roll of crisps and chocolate bars. She's a plate-clearer too, snagging leftovers from anyone nearby. And she appears to pack away three days of calorific intake between Friday evening and Saturday lunchtime. Brother Stuart, on the other hand, eats like a boa constrictor, cramming down a gargantuan meal late at night and then falling into a light coma while he digests it. He also likes to add fat to his considerable intake of dietary fat, slathering mayonnaise on to the chips that come with his triple cheese burger. "That never crossed my mind," he said, when he was informed that this last item alone added 1,319 calories to his intake. That's because you're an idiot, Stuart. Sorry... I do apologise. I meant to say ill-informed.

I approached Felicity Kendal's Indian Shakespeare Quest like a mongoose sidling up to a cobra. For one thing, I'd recently been bitten by the silly Shakespeare in Italy. For another, I have a strong allergy to "quests" and a mild allergy to Felicity Kendal's winsomeness. But it turned out to be a delight – a gratifyingly untidy mixture of cultural history, touching personal memoir and offbeat travelogue. And Kendal really did have qualifications beyond her celebrity for that above-the-title billing. A sweet photograph of her as a mump-faced urchin, playing one of the Dream fairies for her parents' touring company, confirmed her very early experience in sub-continental Shakespeare. Unlike most telly tourists to India she can speak a little Hindi too.

Kendal talked to scholars about the history of Shakespeare productions, including an 1850 Othello that controversially featured an Indian actor in the title role and "set the whole world of Calcutta agog", and revisited scenes from her childhood. And, although Shakespeare himself was mostly seen at a tangent, and sometimes through the opacity of another language altogether, there was a real sense of how his impurity as a writer, the collision of high and low that so dismayed critics of a Johnsonian bent, gave him adoptive citizenship of India. He might not have actually been born in Karnataka, as some of his wilder Indian enthusiasts have theorised, but he's certainly at home there.