Last Night's TV: Three in a Bed, Channel 4<br />Can You Train Your Brain?: A Bang Goes the Theory Special, BBC1

I wonder if Channel 4 thought of calling its latest reality series "Come Sleep with Me". It was clearly after a twist of sexual suggestion, given that they called it Three in a Bed, and since it takes the essential recipe for its very popular competitive dining series – reciprocal sniping – and applies it to a rather more specialised kind of hospitality, the temptation must have been strong. As it happens, though, Three in a Bed isn't brand extension but comes from a different production company entirely – Studio Lambert – which has identified the British B&B as the perfect Petri dish in which to culture samples of social disdain. As with Come Dine with Me, the ostensible subject of the programme – dinner parties in one case and the hotel trade in this – is not really the subject at all. It's simply a disclosing agent for one of our favourite subjects – class.

The machinery is virtually identical to Come Dine with Me. Three sets of B&B owners spend a night at each other's establishments, commenting cattily on the details in private and scoring their stay by paying only what they want. The couple who achieve the largest percentage of their standard rates win the competition, allowing differently priced establishments to compete on a level playing field. So Mark and Claire's frantically aspirational Blackpool B&B, which offers whirlpool baths, 42-inch plasma tellies and remote-controlled lighting, can take on Ray and Joyce from Skegness, who pride themselves on spotless cleanliness. "Our mattresses are Hoovered once a month... we insist on that," boasted Joyce, one of those people who refers to herself in the third person. "Joyce runs a very tight ship at the Kildare," she added, "Joyce has to."

If you're planning a visit it will help if you have the stomach for coy admonition. "If you sprinkle when you tinkle, Be a sweetie and wipe the seatie" read a notice above the lavatory – the kind of winsome touch that will delight some and induce projectile sprinkling in others. The incompatibility of these two groups is what gives Three in a Bed its forward momentum, added to the fact that a B&B is a very peculiar hybrid of public and private space. My home is my castle but for £62.50 a night you can invade.

Roger and Victoria were first up for exposure and early signs did not look promisingly. "Cobwebs, cobwebs... cobwebs," tutted Joyce disapprovingly, running a finger along every horizontal surface. Claire meanwhile was discovering that Roger and Victoria's 16th-century thatched cottage was dismayingly short on mod cons. "We haven't even got a dimmer switch", she said, in the kind of tones you might use if you were to discover a spade and a bucket of sawdust where you'd expected to find the lavatory. Downstairs, Victoria was giving her first impressions of the guests: "They're what I think of as typical seaside B&B owners," she said. "That sounds terribly snobby and I don't really mean it to be terribly snobby at all." Roger, already well lubricated by lunchtime, took them off to see the local tourist attractions, which appeared to consist of some hedgerows and a nearby model village. "It is actually Wimborne.... in model form," he announced, his pitch faltering to a stop after just seven words. Joyce wasn't impressed: "Am I being picky, Ray?" she said. "No you're just being honest," replied Ray. "And that's what Ray and Joyce are. Honest."

I don't think Roger is one of nature's experimenters. He sat out the hokey-cokey at the Tower Ballroom in Blackpool, declined to feed a baby seal a herring at Skegness's Natureland, and took a very dim view of the bathroom television screen in Mark and Claire's five-star boutique B&B. There was a certain amount of tension by now – Victoria got weepy about the comments that had been made about the cleanliness of her rooms ("Don't take it personally... will you?" Claire had said optimistically) and there was a heated tiff about the propriety of Roger going down to B&Q and buying his four rosettes, rather than going through the tiresome business of paying the inspectors to come in with their clipboards.

As the most downmarket of all three establishments, Kildare's chances looked a little slim, and weren't lifted by the Stannah stairlift or the bizarrely detailed visitors information, which included the exact wattage of the two bulbs in the porch and the width, in inches, of the French doors. "Good quality towels, not quite as thick as we would use," said Victoria, who creditably hadn't allowed her desire for revenge to master her truthfulness. She looked for dust and could not find it. Startlingly, both couples then displayed a late swerve into generosity by paying well over the £50 a night Joyce and Ray were charging. Three in a Bed won't change your life, and you may feel in need of a good dusting after watching it. But if you start you're unlikely to stop.

"Can you train your brain?" asked a special edition of Bang Goes the Theory. Only to do brain-training exercises was the answer, a genuine, peer-reviewed finding that was a good result for a popular-science programme. The brain training I'd like to implement now is for whoever chooses the music for the soundtrack. Here's a sequence set in London, so let's have "London Calling" by the Clash. Here's a race between radio-controlled cars so let's fire up the Fleetwood Mac track they use for F1. A bit of lateral thinking, please.