Winifred Robinson is wasted on You and Yours, Radio 4's daily consumer moan. She has a good voice, and a straight way of asking questions, so it's a pity that she spends most of her time discussing such dreary matters as the proposed changes to incapacity benefit, how to bypass an automated phone system, and the price of cashmere. (Actually, I'm quite interested in the last two; but I stand by my position on incapacity benefit.) On 26 January, however, she turns up as the presenter of It's My Story: life in the balance (Radio 4, 8pm), which tells the story of Debbie and Darren Wyatt, who have fought in the high court over the medical care given to their daughter Charlotte. Robinson's approach is devastatingly effective. She prowls around them like a pedigree cat: soft and silky, but with sharp little teeth.

When Charlotte was born prematurely in 2003, doctors diagnosed severe brain, lung and kidney damage and argued that it was not in her interests to ventilate her if she stopped breathing. The Wyatts disagreed, and twice appealed against a legal ruling in favour of the Portsmouth Hospitals NHS Trust. On both occasions, they lost. Then, last October, they won a partial victory. A judge decided that Charlotte could be ventilated; the final decision, however, rested with her medical team. At this point, the Wyatts brought Charlotte home. She requires oxygen and is fed through a tube, but given how far she has come against all the odds, her parents remain hopeful.

The brilliance of this documentary lies in the way it sees beyond Charlotte's deceptively plump cheeks. When we hear Darren bathing Charlotte, he sounds like a softie. Later, we hear him shouting at his neighbours. He sounds like a thug. Darren and Debbie both come from troubled backgrounds; neither of them is in touch with their family (nor is Darren in touch with his three children from a previous relationship). Darren has three other children with Debbie besides Charlotte. When the last of these was born, the two boys went into foster care while Debbie recovered from a Caesarean; the couple have fallen out with anyone who might have helped. When Darren visits Charlotte's doctors, he is accompanied by a guard, at the hospital's insistence. Perhaps this is because he and Debbie once asked the police to investigate the amount of morphine their daughter was being given (no evidence of any wrongdoing was found). Perhaps it has also to do with their having sold their story to the press.

Do I sound judgemental? I do not mean to. Because what this documentary ultimately shows is not so much the fecklessness of the Wyatts, but the way in which, as Larkin has it, man hands on misery to man. Miserable as children, Debbie and Darren then found one another and took on the world. I imagine that when Charlotte was born they enjoyed the attention. For once in their lives, everyone - doctors, social workers - took an interest in them. When this attention slipped, it was doubtless painful.

Charlotte is their daughter and they love her, but she is also their only means of getting any purchase on a hostile world. They deploy her often, and without hesitation. I do not think they do this in a cynical way; they do it because they don't know what else to do. That it takes Robinson and her team a mere half-hour to fathom this deepening of the human coastal shelf is, I think, a minor miracle of journalism. She is thrown away on fabric softener and train tickets. She needs a proper gig.