Five Days, BBC1

It's become something of a truism to suggest that when it comes to television drama, the US wipes the floor with our home-grown output. While channels such as HBO, AMC and Showtime have put cinema snobs in their place with offerings that are variously risk-taking, adrenalin-raising and novelistically nuanced, over here we are generally grateful for anything that doesn't feature bonnets, scalpels or Max Beesley.

It's right, then, to applaud the recent phenomenon of the "event drama": mini-series such as the BBC's Criminal Justice and ITV's Collision which are "stripped" over consecutive nights, layered with multiple narratives, heavyweight actors and hot-button issues, and primed to be showered with awards. Gratifying as all that Americanised ambition has been, though, I wonder if we shouldn't hold off the champagne for the moment.

Take Five Days, writer Gwyneth Hughes's sequel to her 2007 police procedural saga of the same name, which blazed a trail for this grandstanding, time-demanding trend. Running from Monday to Friday, it kicked off with that old crime fiction chestnut, a pair of seemingly unrelated but obviously related incidents: the apparent suicide of a Muslim woman throwing herself in front of a TransPennine train and the abandonment of a baby at a nearby hospital. Then as passenger and off-duty police officer Suranne Jones stepped up to detective duties, so a web of interconnected characters was spun around her. There was Bernard Hill's enigmatic fellow passenger, who happened to come with a backstory that left him enamoured of Jones's Alzheimer's-afflicted mum; David Morrissey's maritally troubled sergeant, whose mischievous son happened to be a chief witness to the suicide; Matthew McNulty's sweet-natured conductor, who happened to be a white Muslim convert desperate to adopt a Muslim baby; and Steve Evets' haunted train driver, who happened to ... well, let's leave it there. Suffice to say, this purported to be a standard-issue whodunit fused with a state-of-the-nation treatise, touching on everything from racial integration and terrorism to institutional chauvinism and care of the elderly.

Problem was, the fusion often jarred. On the plus side, the script contained fantastic individual moments: an early exchange between Jones's cautiously PC PC; her foot-in-mouth mum; and a Muslim cab driver offered a masterclass in social observation. There was also a wonderful honesty in the way Jones and Morrissey's will-they-won't-they romantic tension climaxed, not in quivering declarations but in a sozzled Morrissey's bald proposal: "I suppose a fuck's out of the question, then?"

Performances were uniformly outstanding: ex-Corrie star Jones anchored proceedings with an effortless and world-weary charm, while, of the rest, special mention must go to Anne Reid, whose outwardly wittering but inwardly stoic portrayal of a woman facing up to mental decline was deserving of its own Alan Bennett Talking Head.

Undoing all this fine, truthful work, however, was a story that moved from barely tolerable contrivance to flagrant implausibility. If you had incriminating snaps of yourself at a terrorist training camp, would you: a) leave them in the "My Photos" folder of your laptop; and b) leave that laptop logged on in your family's living room? Did we really need two separate plot developments to hinge on Jones randomly bumping into people on station platforms? And, call me an uncreative liar, but how did one clearly Caucasian character manage to trick her lover into believing she was Asian?

Finally, as the central mystery concluded with an almighty whimper, you couldn't help feeling the programme, like Criminal Justice and Collision before it, had fallen between two stools: too earnestly high-minded to function as a compelling potboiler, and yet too hokey to leave any more profound an impression. And while this short-order, week-long format is all well and fashionable, it seems too limiting to be anything more than a scheduler's gimmick. To look to America's example again, what about an ambitious, contemporary British drama not "stripped" but, rather, teased out across 13, 15 or 24 episodes and as many weeks, where characters and ideas might be allowed some room to breathe? Now that would be an event worth tuning in for.