Last Night's TV: Dirk Gently/BBC4<br />Jamie Christmas Lock-in/Channel 4<br />Nigella Kitchen/BBC2

I have no idea how loyal the makers of BBC4's Dirk Gently were to Douglas Adams's Dirk Gently's Holistic Detective Agency, though I'd hazard a guess that a few liberties have been taken. The iPhones and Blackberrys were one giveaway; the various references to East 17 another. And, of course, the book's title has been truncated. Does it matter? Probably, to some of Adams's more devoted fans. In the context of last night's viewing, though, I'm inclined to think that for most of us it doesn't. Not a jot. Gently was so jolly, so rollickingly good natured, that to complain over such trivialities seems terribly poor form.

Gently is a detective. More than that: he is a holistic detective. He believes that everything is interconnected. And so when, on being hired to investigate the disappearance of an old lady's cat, he ran into an old friend from university, he was certain it was a clue. In a way, it was. The pair teamed up, tackling the triple mystery of Henry the cat's whereabouts, the departure of a businessman from a nearby warehouse, and the failing love life of MacDuff (the friend). What followed was a cartoonish series of escapades that saw Dirk prove his creativity, if not sleuthing skills, with his Scooby Doo-esque plans. He faked suicide to steal a set of psychiatric records, he hypnotised MacDuff to take him back in time (not literally, though there is some of that) and he pretended to be a patient at the practice of MacDuff's girlfriend. He found Henry, sort of – and a lot more besides. That nice old lady who hired him, for instance? Not quite as nice as she seemed.

Stephen Mangan – hitherto best known as Guy Secretan from Green Wing – was ideal casting as the hapless Dirk, and Darren Boyd just as perfect as MacDuff. Helen Baxendale, too, made a welcome return as MacDuff's disgruntled girlfriend. In fact, there wasn't very much you could fault about the production at all. Right down to the quirky camerawork and youthful, poppy soundtrack (who would have thought the Hoosiers could be so right in any situation?), the director, Damon Thomas, got it pretty spot-on. The result was a pleasingly festive-feeling adventure; part Wallace & Gromit, part Doctor Who, part The Secret Seven. And the best thing? There wasn't a Christmas tree in sight. Douglas Adams once claimed that Gently would make a better film character than his more famous hero, Arthur Dent. Based on last night's experience, he may well have been right.

Jamie Christmas Lock-in sounds like a good idea, doesn't it? What with him having nigh-on national treasure status and those Sainsbury's ads looking so nice (you know the ones: mince pies all rustic, served to a crowd of children with blobs of crème fraîche and slivers of orange peel). Well, it wasn't. It wasn't a good idea at all; indeed, it may well have been a very, very bad one. Oliver – thanks either to too much time spent in America or the excitement of this curious faux-live format – morphed from nice lad next door to shouty television host who's going TO COOK ALL THE TURKEYS and put EMPHASIS on RANDOM PHRASES. Speaking of which – hello, Jonathan Ross. Fancy seeing you here, promoting your new show.

In between the yelling and the celebrity appearances (Charlotte Church got some time, too, teaching Oliver to make a cheeky Vimto and waltzing across the bartop to pour champagne), Jamie did what he does best: cooking. There were more manic as-live bits – baking turkey in a cave of salt and making the perfect burgers with Louie Spence – but there were some more palatable pre-filmed sequences, too. Then, the Jamie we know and love re-emerged, singing the praises of baked camembert with cranberries and showing us yummy smoked salmon on toast. It's just a shame there wasn't a bit more. Nice Jamie had barely settled on-screen before he was whisked away by his manic alter ego. Instead, we got a spoof commercial for an Oliver fragrance ("Jay Mange" – edible and wearable) and a hidden-camera series in which viewers suggested ways they'd like to see him die. Boiled in a pot was one particularly good answer. After last night, it sounds like rather a good idea.

It's almost Christmas, which means that it's almost time for Nigella to leave our screens and disappear off into that photogenic study of hers to pen next year's bestseller. Sob! Ah well, there she was last night, in the penultimate episode of Nigella Kitchen, doing her best to cheer us up with some tortilla chips and an Americano. Not the coffee, dummy, the cocktail. "I'll have you know that this was James Bond's original drink," she teased. Of course, it's all faintly ridiculous: the gorgeous hostess, with her gorgeous lifestyle, her gorgeous kids and that gorgeous use of metaphor. But to mutter such scepticisms is to underestimate just how compelling Lawson is. She's irresistible: few other celebrity cooks provide quite such straightforward viewing pleasure.

Naturally, it wasn't just booze on offer last night. "Devilishly Good" was the theme and so, of course, we got a devil's food cake, choc(olate)-a-block with finger-licking photo opportunities. Less obvious were Lawson's easy-peasy roast duck legs and her French toast with stewed plums. Not that she was having any of it. "I'm going back to bed to finish these off," she purred. Oh, Nigella. Please never do a lock-in.

a.jarvis@independent.co.uk; twitter.com/aliceazania