The life and fiction of Rosamond Lehmann were in many ways indistinguishable from a superior Mills and Boon: there were dark and difficult heroes and relationships that had to be waited and worked for. Where Lehmann parted company with the template of popular romance was in her endings. Things had a habit of turning out badly, for both herself and her heroines. Terrified of being abandoned, even at the age of 17, Lehmann finished her long life still looking for the one true love who would not let her down.

It is hardly surprising, then, that critical posterity is divided as to the merit of novels such as Invitation to the Waltz, Dusty Answer and The Weather in the Streets (there were only seven in total - all those affaires ate into Lehmann's writing time). For some readers, Rosamond Lehmann is the true heir of Virginia Woolf, and the writer who fulfilled the demand for a literature that retold the world from a woman's point of view. For others, she is a minor talent who would be forgotten completely now, were it not that, luckily, Virago came along to reprint and reposition her as an unlikely icon for the early 1980s. Her prose, according to which camp you are in, is either an exquisitely sensitive barometer of female subjectivity, or else a stream of overcooked mush with neither shape nor relevance.

Selina Hastings does not go too deeply into these matters, and it may be that she is right to leave the assessments of Lehmann's achievement to other voices and different contexts. Instead, Hastings concentrates on straightforward biography, telling a story that runs in close parallel with that of Olivia Curtis, Judith Earle and all those other ardent, thwarted girls who suffer and flop through Lehmann's fictional world.

Rosamond Lehmann was born the day after Queen Victoria's funeral in February 1901. She had what should have been a sunny, secure, upper-middle-class childhood on the banks of the Thames. But something cannot have gone quite right, especially concerning her relationship with her parents. She knew she was neither the favourite of her charming father Rudolph (he preferred her younger sister Beatrix, the actress), nor her brisk mother from New England, Alice, who doted on her brother John, the publisher. As a result, she moved into adulthood with a permanent ache for love. While at Girton, to which she won a scholarship, her emotional hunger caused her constantly to misjudge situations. A young man who kissed her after a May ball was astonished to receive a letter a few weeks later demanding to know why he was ignoring her. In fact, David Keswick was already engaged to another girl whom he had known since Eton. This rejection set the pattern for all Rosamond's subsequent romantic relationships.

Only her extraordinary beauty - alabaster skin, jet-black hair turned prematurely white, and a figure that was perfect except for a pair of thick ankles - kept Lehmann emotionally afloat. No matter how draining her demands and unreasonable her expectations, there were always men willing to take her on. After a brief, sexually malfunctioning first marriage, she wed the artist Wogan Philipps, who, as heir to a baronetcy, was perfect romantic hero material. When this second marriage began to fail, despite the arrival of two adored children, Rosamond started an affair with Goronwy Rees, the Welsh chancer who may or may not have been spying alongside his best friend, Guy Burgess. In a painful reprise of the Keswick affair, Rosamond discovered that her relationship with Rees was over only when she saw a notice in the Times announcing his engagement to someone else.

All this Sturm und Drang, however, was only a proving ground for Lehmann's most celebrated passion. For nearly a decade, she nagged and begged Cecil Day Lewis - yet another impossibly good-looking intellectual prince - into loving her. But no sooner had Day Lewis finally agreed to leave his wife and family to be with Lehmann than he dumped her for a younger lookalike, Jill Balcon. Lehmann's furies were as violent as her loves: having taken revenge on Rees by shopping him to MI5, she got her own back on Day Lewis by slapping him hard at a Chatto & Windus party.

Her late-flowering interest in the spirit world, precipitated by her daughter's early death from polio, gave Lehmann a new arena in which to cajole and scold all those whom she felt had let her down. Day Lewis, who died in 1972, came through to say how sorry he was for being such a beast, while the shade of Virginia Woolf admitted that she had been wrong to be sceptical about life after death. Lehmann's living friends, meanwhile, looked on in tactful silence as she worked on her last book, a spiritual autobiography, which, although dotty in its logic, was written in prose that had lost none of its graceful shimmer.

Selina Hastings, who knew Lehmann in her querulous later years, has produced exactly the right kind of biography, as delicious as the chocolates on which her subject feasted at every opportunity (Lehmann ended up huge and puffy, all traces of beauty smothered under layers of fat). In particular, Hastings is an acute reader of the social and emotional contexts that fashioned Lehmann's neediness and snobbery; and she is perceptive, too, on the way she manipulated anyone who strayed into her overheated world. Most important of all, however, she makes you want to go back to the novels and think again about whether they matter and, if so, why.

Kathryn Hughes is a biographer and critic