Last Night's TV - Agatha Christie's Marple, ITV1; Coronation Street, ITV1

She's still on the right trail

Christmas television, rather like Christmas itself, is a blend of trends and traditions. And the tradition is to indulge the trend, so that whatever might be the format du jour - game show, talent show, reality show, panel game, nostalgia fest – is given pride of place in the schedules. Nothing gobbles up those schedules quite as satisfyingly, though, as drama. No matter who's been foxtrotting, eating witchetty grubs or singing Christmas Cowells, drama is and always has been the sine qua non of festive-season telly. It's good for us, the viewers, and it's good for them, the broadcasters. For not only does it very usefully occupy up to two hours of primetime, it also shows that they have been spending their money, which, one way or another, is also our money, creatively.

But there is original drama, and there is Agatha Christie. I don't know anyone who still refers to the BBC as Auntie, but we should all call ITV Agatha, especially at this time of year. When they hear the distant tinkle of jinglebells, ITV executives simply dial M for Marple. Or P for Poirot. On Christmas Day, Hercule Poirot was let loose on the Orient Express, and last night Miss Marple wound up at Chimneys, a grand country house owned by Edward Fox, who was not only born to wear a wing collar, but very possibly born wearing one.

I confess to being fascinated by Edward Fox. Did any actor ever play the same character so many times, with so many different names? I suppose the late Robert Morley might have given him a run for his money, as might James Robertson Justice. But not even those two irrepressible old hams had the longevity of Fox, who give or take the switch of a monocle from one eye to the other, has been playing Edward VIII, with or without Mrs Simpson, since 1978.

I don't mean this as criticism. For one thing, I am truly in awe of the ability to make limited talent go an extraordinarily long way. And for another, he plays that character better than anyone. When they came to cast The Secret of Chimneys, and had to draw up a list of contenders for the part of stuffy old patrician Lord Caterham, I'll bet it was a list of one.

You have to hand it to the producers of these big Agatha Christie extravaganzas; they don't half cast them well. On Christmas Day, the Orient Express chugged along bearing Eileen Atkins, David Morrissey, Hugh Bonneville and Barbara Hershey, not to mention dear David Suchet. And as well as lovely Julia McKenzie, Chimneys belched out Dervla Kirwan, Stephen Dillane and Michelle Collins, as well as, intriguingly, both Ruth Jones and Mathew Horne, Gavin & Stacey's Nessa and Gavin.

They were all simply splendid, taking perfectly in their collective stride a plot of sublime silliness that I'm pretty sure bore scarcely any resemblance to anything Dame Agatha ever wrote. I suppose the trick to these things is to play them completely straight. Even the slightest whiff of a suggestion that an actor might be treating it tongue in cheek, and it would all come apart at the seams, which on reflection is a pot pourri of mixed metaphors that might almost sit on Miss Marple's window sill back in St Mary Mead. The point is that we can chuckle our way through it but they mustn't, even though last night's investigating officer, Inspector Finch of Scotland Yard (the ever-excellent Dillane), might just as easily have been Ronnie Corbett's Inspector Corner of the Yard.

As for what actually happened, if you watched then you already know and if you didn't, you really don't need to know. Suffice to relate that we got a shot Austrian count, a poisoned housekeeper, a famous lost diamond, a secret passage and some sumptuous production values. Oh, and the double-murderer turned out to be Edward Fox, nursing a 23-year-old grudge involving his dead wife and a Viennese waltz too far. Did I say Edward Fox? I meant Lord Caterham. Or did I?

Whatever, you could have taken away the wing collars, moved the action to Greater Manchester, made Lord Caterham a bookie, and, hey presto, an episode of Coronation Street. The trouble with the great Weatherfield tram disaster of 2010 is that, soaps being soaps, everything has to return to normality a little too quickly to be entirely plausible. Did I say entirely? I meant remotely. After all, it's barely three weeks since septuagenarian Rita Sullivan (Barbara Knox) was buried under a ton of rubble, and while I for one am chuffed to bits that Rita is still alive to dispense the lemon sherbets, the rudeness of her health stretches credulity well beyond twanging point.

Still, Coronation Street has always offered far more delights than irritations, and sniff as we might at Rita's Lazarus-like comeback, not to mention that of Peter Barlow (Chris Gascoyne), who wasn't so much at death's door following the tram crash as over the threshold and into the parlour, it's hard to think of any plot development in any drama over the Christmas period quite so appealing as Kevin Webster's discovery last night that his cuckolded wife, Sally, had left him nothing in the food cupboard except one can of lobster bisque and another of bamboo shoots. Besides, if plausibility were the be-all and end-all of drama, then Shakespeare himself would have been found wanting. What we require, especially at this time of year, is escapism. Those lively old broads Jane Marple and Rita Sullivan fit the bill perfectly.