Last Night's TV: Dive, BBC2Underage and Having Sex, Channel 4Homes from Hell, ITV1

Argh. Sex education. Yuck to that. Not the sex bit, I mean. The education bit. The bit where sex meets school teacher, strikes up a conversation and before you know it – bam! – has persuaded her to sacrifice all dignity. Look, there she goes again, showing us how to wrap a banana in a condom. Not that it isn't all Very Important Indeed. Obviously. Of course it is, and we need more of it, or we'll end up a nation of teenage pregnancies and unwanted children. The more condoms on bananas the better. Or something. God, sex ed's awkward, isn't it?

Dive, however, just about makes it bearable. Much more than bearable, in fact. The first part of this two-piece drama from BBC2, written and directed by Dominic Savage, was a pitch-perfect depiction of young, modern, British puppy love.

Lindsey (elegantly played by Aisling Loftus) is an ambitious young diver whose entire existence is geared towards securing a spot at the 2012 Olympics. She is woken up at 6.30 every morning, driven to diving by her dad, and then taken to school. When her friends head out to drink in the park, she turns them down in favour of the pool. And then her dad leaves, replaced by a younger model, who has been moved in by her chronically flaky but well-meaning mother (the ever brilliant Gina McKee).

The event proves a trigger to a string of misbehaviours: hanging out with friends in the park, flirting with boys and having unprotected sex with swoonsome schoolboy Robert (another stellar performance, this time from Jack O'Connell). Anyway, as you'll already know if you managed to catch Underage and Having Sex (on which more later), unprotected sex doth a pregnancy equal. Such was poor Lindsey's fate.

She dealt with it all remarkably calmly, though not necessarily very well, opting to bottle it up instead of actually talking about it. She continued her diving training and tried out for the Olympic team (which she appeared to make) as if nothing had happened, telling no one, then, suddenly, blurted it out midway through an argument with her dad.

The whole thing was shot using the kind of aqua palette that the title would suggest. The opening scenes showed Lindsey training, elegantly, in a bright blue pool. There were shots of the sky, shots of the sea, of glaucous plunge pools and teal diving boards, frequently accompanied by a gentle, chiming, ice-cream van soundtrack. Loftus is perfect as Lindsey. She doesn't just look like McKee – pale, quietly beautiful, almost Russian doll-like – but shares her calm, poised sense of delivery, coupling it with the kind of teenager's innocent worldliness that can be difficult to recreate on screen.

Tonight, we get a look at Robert's side story, though, judging from the trailer, not Robert's side of what's already been, but Robert's side of what happens next. And I can't wait.

Nothing in Underage and Having Sex should have been surprising. Everyone knows that children have started having sex young – that's why the teenage pregnancy rates are so high, and why youngsters make front-page news before they have their 14th birthday. Still, hearing Christopher (who is 13 but looks more like he's eight) confess that he started having sex with his girlfriend over a year ago was undeniably weird. Much more than that, actually, it was really quite distressing, particularly seeing as Christopher and his girlfriend appeared to spend all the time that they're not having sex doing incredibly sweet, childish things, like running along the river, skimming stones across the surface. Amazingly, Christopher's mum managed to persuade him to stop, by explaining her own regrets over losing her virginity at a comparatively ancient 14. Christopher, it rapidly emerged, was remarkably switched on for his age. When his mum made her case, he listened, carefully nodding at each point. And it worked! Two year later, we revisited him – and he'd not had sex since.

For those who couldn't bear another lesson in safe sex (though they were available courtesy of The Sex Education Show), there was the option of design and technology, or economics, or something from ITV1's Homes from Hell. God, it was depressing. In more ways than one. The production has all the flair of a late-night makeover show (complete with title sequence that even the most computer illiterate of toddlers could create, given a desktop and pointed in the vague direction of the "on" button). The idea has obviously been around for a while (this isn't the first series, after all). Still, I did find myself fairly absorbed, if not by the programme's merits then by its sheer grimness.

The tales we heard were unrelentingly bleak. Possibly the most heartbreaking was David, the retired concert pianist who had poured all of his savings into a home in Portugal where he planned to move with his partner. He had (naively) agreed to pay a local builder more than £200,000 in four instalments, with the promise of the house and land being put into his name once the fourth had been transferred. Inevitably, the building work stopped after the third sum went through – and the ensuing stress spelled the end of his relationship. Now he has no ownership deeds, no savings, no holiday home and – most poignant of all – no space big enough to hold his piano. On second thoughts, sex ed doesn't sound so bad after all, does it?