Review

A father is playing "What's the time Mr Wolf" with his children, walking away with cartoon ponderousness before spinning round to seize the nearest child, who screams in delicious, synthetic fright. But the children are naked and another dread stalks the scene. Is that grasp entirely paternal? Might those screams turn serious?

Leanne Klein began and ended her unnerving Witness film (Channel 4) with scenes that 20 years ago would have been innocuous, an easy emblem of purity, but which are now inflammatory, tainted by thoughts of incitement or impurity. And by the time you reached that final pantomime of childish fears, you had been effectively corrupted yourself, stained by the anxiety of a crime for which almost anyone will now serve as "the usual suspect".

Is this paranoia or a long-overdue vigilance? The statistics don't help at all: more than a thousand families a week are now investigated for suspected sexual abuse, and yet fewer than one in seven investigations find a child to be at risk. And even here there is no firm foothold - much sexual abuse leaves no physical evidence, as one social worker pointed out, and it is easy for an abuser to coerce children into silence with the threat of family break-up. So it's almost impossible to know whether we are looking at an unprecedented vandalism of family life or a losing battle against the exploiters. Klein's film was about the queasy, unceasing swell that such alternatives set up, one that she represented by cutting between those who had real cause to fear such accusations and the work of Bradford Social Services, who must investigate every "referral" in an attempt to sift truth from malicious lie.

What connected the two was the sense that the presumption of innocence had been damaged beyond repair. Hearing one of her charges say "My daddy hurts me when he wipes my bottom", a playgroup leader called in the social services. The child's remark that "licking bottoms is rude" was then enlisted, not as a casual repetition of an innocent conversation about dogs in a local park, but as "age inappropriate behaviour" - a truly chilling story for any parents watching, their minds nervously reviewing the lavatorial fascination of the normal three-year-old. There is no acquittal from such charges - only the accusing verdict of "insufficient evidence".

On the other hand, the beleaguered social workers had been bruised by knowledge into a nagging fear that someone might escape. "I would far rather slightly infringe somebody's civil liberties to try and establish the safety of a child than be afraid to do so and leave the child in jeopardy," said one melancholy social worker. It was an unexceptional statement, until you remembered that children have their liberties infringed by pervasive suspicion, too.

His relationship with his own daughter had been deformed by the habit : "I do not wash my daughter - she washes herself, she's four - and I haven't since she was a baby," he said. The reason for this self-imposed detachment was not a fear of what others might think - as it was with the divorced father who avoided any intimacy that might be misrepresented - but a sort of preventive mistrust of what might lay concealed in himself. He had heard too many abusers explain that their own crimes began on the slippery slope of bathtime, he said.

When you thought your paranoia could not be twisted any further the film gave one last surprising wrench, a real thriller revelation. The principal case it showed being investigated involved accusations by a step-parent and mother against the biological father, a suspicion bolstered by the new boyfriend's anxiety about the way the little girl sat in his lap. But when the social services researched a little further, tapping into the police computers, they discovered that the accuser had a record of sexual assaults on young girls and the mother had been abused as a child herself. Even sounding the alarm, it seemed, might be evidence of guilt. Quite properly there were no facile scapegoats here, just a powerful sense of unfixed horizons which left you feeling sick and uneasy.