If anything was going to put you off your Ferrero Rochers over Christmas, it had to be The Fattest Man in Britain, ITV's comedy drama about a man in an orthopaedic armchair eating himself to merry hell. Timothy Spall looked dangerously at home in the title role as Georgie, with comedian Bobby Ball admirably cast as his "manager", Morris, turning up with a cabful of Japanese tourists eager to take pictures and lay their hands on the big man's folds. "I would ask you to respect Georgie's private zones," said Morris (though, frankly, you imagined these people might get enough blubber at home). Frances Barber completed the homely trio as Janice, who came in every day to shovel Georgie's meals together and grease his legs, which was as attractive as it sounds.

With Caroline Aherne co-scripting, there was as much pleasing northern drollery as you'd expect amid the ill-lit claustrophobic clutter and junk food and trash TV familiar from The Royle Family, though admittedly the oxygen tank looked ominous.

Things took a turn when a crew of youths was sent by the social services to tidy the garden and Amy - a pregnant teenager on the run from a violent boyfriend - ended up moving in. Aisling Loftus was excellent as the underfed, beaten waif looking for a father figure and finding it in kindly Georgie. There was a worrying moment, in his late mother's bedroom, when you wondered what kind of a comedy this was turning into... but no, Amy was soon settling in, cooking and tidying up, nibbling a dark chocolate Magnum with Georgie (not the classiest of product endorsements), helping Janice with his pig-sized legs and restyling his terrible 80s mullet - an early clue that he hadn't been out in 23 years. That's how long it had been since his mum died. "It's like I was eating for her," Georgie confided. "Like there was an angel on my fork."

All was well until a rival barrage balloon from Birmingham challenged Georgie to a TV weigh-in and Morris - aided by locals arriving with mountains of pizza and bakewell tarts - set to bulking him up for the contest. Amy - now almost as big as Georgie (well, not quite, but who remembered she was even pregnant?) - railed against the freak show that would surely kill him.

Events were channelled into a poignant denouement, but when the baby died and Amy called it a day with Georgie, it didn't feel like tragedy. Even when Georgie rose from his chair and struggled down the street to see her, it was more Love Actually than love. There was a late attempt at profundity with a short disquisition about the desire to make failure look like success. "If I'm not the fattest man in Britain, what am I?" cried Georgie. "I'm just a fat man!" It was a great line, but it just made me think that inside this broadly entertaining drama was a sharper, less funny one trying to get out.