Rachel Cooke revels in a Beeb biopic that explains a complex love triangle.

Off the top of my head, I wrote down a list of all the people whose lives BBC4 has turned into films: Hughie Green, Fanny Craddock, Kenneth Williams, Enid Blyton, Frankie Howerd, Gracie Fields, Margot Fonteyn, John Lennon, Harry H Corbett, Barbara Cartland . . . it's quite long. Even as I write, some poor sod is busy transforming himself into Kenny Everett, giant plastic breasts and all.

If the BBC goes on like this, it'll soon run out of subjects, at which point it could all get quite comical. Prepare yourself for biopics of Richard Whitmore (1970s newsreader who went on to star with Bernie Winters in a UK tour of Underneath the Arches) and Nerys Hughes (annoying Liver Birds actress later immortalised in the Half Man Half Biscuit pop song "I Hate Nerys Hughes").

When he took over from Janice Hadlow as controller of BBC4 in 2008, Richard Klein defended the station's reliance on this singularly weird genre. "As a small digital channel, it's hard to get anyone to come and watch pure fiction that no one has heard of before," he said, somewhat inelegantly. "Basing our dramas on factually based stories, we can re-examine and reinterpret, but people already have an interest." This is only half the story. The beauty of the biopic is that the dead cannot be libelled - which is why, of course, poor old Richard and Nerys, both of whom are still alive, are safe for the time being. The juice in a "troubled" life can be made all the juicier by the writer, without any worry that he will have to account for his accuracy (or lack of it).

Is this a good thing? Well, if you're the son or daughter of the subject of a biopic, it must seem like a rather bad thing; even as a viewer, these films can make one feel uncomfortably prurient. But sometimes fiction - or at least, imagination applied to decent research - also takes you nearer to the truth, or what you feel to be the truth, than facts. This is exactly what I felt as I watched Hattie (19 January, 9pm), a film about the outré domestic arrangements of Hattie Jacques (for a time, Jacques shared a house with both her husband, John Le Mesurier, and her younger lover, a car dealer called John Scho­field; Le Mesurier lived uncomplainingly in the attic until their divorce in 1965).

I knew about this ménage, but the film made me understand it; previously it was unfathomable. I realised that it wasn't diffidence or masochism on Le Mesurier's part that made him put up with so much, but love. Nor was Hattie, as I'd assumed, a self-obsessed sadist. She loved him back and must, when he left, have missed him mightily. His replacement - sexy but dim and posturing - was no substitute at all. Because I loved Jacques and Le Mesurier as a child - the Carry On films and Dad's Army were and, for all I know, still are beloved of children everywhere - I found this touching. Even the worst BBC4 biopic is wonderful on period detail, and this one was no exception. The Jacques-Le Mesurier household was replete with 1960s Midwinter teapots and Ercol shelving, and everyone looked perfect: fag in mouth, gin in hand, torso in girdle (I mean the women; the men wore beige knitwear).

It was the central performances, however, that were special. Ruth Jones is more beautiful than Hattie was, but otherwise she was just right: I believed in her, whether her curves were swathed in taffeta (the public Hattie) or nylon (the housewife Hattie). She exuded kindness but also an embarrassed sort of need (the dialogue was minimalist - this being the England of the early Sixties - and nothing was ever fully articulated).

Even better was Robert Bathurst as Le Mesu­rier, who suggested, by means of a series of tiny movements across his face, that beneath the shy and well-mannered exterior lay great reservoirs of feeling. "Oh, you poor thing," he said to Hattie as she confessed her guilt. His words seemed to teeter for a second on the brink of sarcasm, but then you saw his eyes and you realised that he meant it. He grasped that his lovely wife, in the throes of a new sexual obsession, while never having ceased to love her husband, was in a bind, and he decided in that moment not to tighten the knot if at all possible. What a gent.

Rachel Cooke trained as a reporter on The Sunday Times. She is now a writer at The Observer. In the 2006 British Press Awards, she was named Interviewer of the Year.

This article first appeared in the 24 January 2011 issue of the New Statesman, State of Emergency