The Weekend's TV: Appropriate Adult, Sun, ITV1

Appropriate Adult opened with two intercut visions of early-morning banality.

In one, a large family clattered their way into the day, with shouts about lost rucksacks and sibling bickering and requests for clean shirts. In the other, a middle-aged woman shuffled to the television in her fluffy slippers for the first fag of the day, the camera sidling along the sideboard as she went, past the three wise monkeys and a kitsch framed birthday card: "A Mother's Heart Is Like a Rose. Always Open, Always Loving". Both households are about to have their routines shattered. In the first, it's because the mother, a trainee social worker, has been called in to serve as legal chaperone for a recently arrested man. In the second, it's because the mother is Rose West, and it's her husband Fred who's sitting in a Gloucester police cell.

With West as a central character it was inevitable that the blandly bureaucratic title of Neil McKay's drama would have taken on some extra meanings. The question of whether it was appropriate for such a film to be made at all has already been raised in various places, and focused principally on whether anyone is entitled to appropriate the terrible experience of the families of those who were killed. So, was it exploitative? Well of course it was. It exploited our perennial (and slightly shamefaced) desire to know the worst – the impulse to stare into a bottomless pit and wonder just how deep it goes. If the drama had been interested only in the legal nicety of providing vulnerable people with a proxy guardian, then it never would have made it on screen. Like it or not, Fred West's star attraction gave the green light.

The more pertinent question is whether it exploited our interest to any good purpose. A final verdict on that may have to wait until next week but for the moment there's no denying the drama's grip, or the compelling oddity of the relationship it explores. Janet Leach's role as appropriate adult was to "facilitate communication" with West, and she very quickly realised that she'd opened an unmarked door into hell. "So I got this ice saw," says West matter of factly, explaining what had happened to his daughter Heather, "and I cut her legs off and that was... unbearable.. I can still hear that in my sleep. Then I cut her head off... I closed her eyes first because, well, you're not going to take a saw to your own daughter when she's sat there looking at you, are you? And then she fit neatly in the bin." As she listened to him, tipping his hat to the common decencies of dismemberment, Emily Watson's face paled in front of your eyes.

As an adult, West would only have required an appropriate adult if he had learning difficulties. Whether the police really believed he did or not is slightly fudged here but in Dominic West's performance, he comes across as an odd mix of manipulation and guileless stupidity. He has no grasp of scale, so that he can leap from atrocity to small talk in a sentence, unaware that he's crossed a divide everyone else in the room finds unbridgeable. And he displays the instant, sentimental self-pity of a monster – outraged that his love of his children can be called into question, even as he's in the middle of confessing to killing some of them. He also enjoys playing with Leach, implying a fellow-feeling between them and taunting her with confessions that she knows – because of her duty of confidentiality – that she can't pass on. "I know that you haven't always been properly loved and respected by men," he says at one point, and West shows the calculation in his eyes as he gauges her response. This is a man who doesn't feel emotion, but knows how it can be used as a crowbar.

The drama hints that Leach was instrumental in getting West to confess to more murders, demanding his candour as the price of her continued attendance. It also explores the immediate cost to her family life, as she moved without decompression from the depths of human depravity to domestic routine. But it hasn't yet quite dared to probe what kept Janet Leach going back, even as her own husband struggled with a bi-polar condition. When it's hinted that she might want to withdraw from the case, she reacts with an almost panicked indignation. Is it possible that she just found it too exciting to have privileged access to a story that had become a media obsession? In not looking closer at that question, Appropriate Adult missed an opportunity to question our appetite for atrocity, rather than just feed it.

t.sutcliffe@independent.co.uk