Virginia Woolf and Vita Sackville-West were lovers. Does that mean they had sex? It probably does, because Vita liked sex and was a pursuer of women. She also enjoyed a long and successful marriage to Harold Nicolson. He too had his affairs. Virginia and Leonard Woolf were largely compatible and certainly affectionate. It seems unlikely from all that we know that she was interested in sex with Leonard, but sexless marriages were, and are, common enough. The thing about passion is that it is much more than a sexual encounter. And that is worth keeping in mind in the case of Woolf’s novel Orlando. What Vita and Virginia did or didn’t do in bed is much less important than the effect of Vita on Virginia’s imagination.

Had the love affair not happened Orlando would never have been written. That would be a loss. As Woolf wrote in her diary: “A biography beginning in the year 1500 and continuing to the present day, called Orlando. Vita; only with a change about from one sex to the other.”

Orlando is not the first piece of fiction about a sex change. Ovid’s Metamorphoses is a playful and serious treatise on the shiftability of form – especially human form, as humans turn into trees or animals, or the gods embody themselves as human to pursue their love interests. In The Arabian Nights, there are both gender switching plots and cross-dressing. Shakespeare loved gender disguises – a girl who’s a boy who’s a boy who’s a girl – and of course as women were not allowed on the London stage in Shakespeare’s day, every female role was cross-gender. Every romance is a bromance.

It is likely that the title of Woolf’s novel comes out of As You Like It, where the heroine Rosalind disguises herself as Ganymede, and in that guise teaches the man she loves – Orlando – how to love in return.

Sackville-West liked to cross-dress, calling herself Julian. The freedom of male dress and male privilege is inverted in Woolf’s biography, as Orlando as a woman discovers how cumbersome are the clothes she must wear, and how restricted are her freedoms.

Facebook Twitter Pinterest Virginia Woolf, left and Vita Sackville-West. Composite: AP/Getty Images

Woolf’s Orlando begins his journey as a young man living at Knole, the great house in Kent that Sackville-West could not inherit because she was female. The novel starts in an attic, as the young Orlando slices at the preserved head of a Moor. It also begins with a famously disingenuous sentence: “He, for there could be no doubt about his sex … ” and then we spend the rest of the novel doubting exactly that.

Is Orlando the first English language trans novel? It is, yet in the most playful way. Orlando manages his transition with grace and a profound truth. On seeing himself as a herself for the first time in the mirror, she remarks: “Different sex. Same person.”

That difference of sex, though, had legal and social implications. Many of the men Woolf knew, including her husband Leonard, and her sister Vanessa’s husband, Clive Bell, had been educated at Cambridge. Virginia and Vanessa had been home schooled; the usual method for upper class girls. Other girls were barely schooled at all.

When Woolf was writing Orlando, more than 8 million women aged 30 and over had won the vote in the 1918 Representation of the People Act. For men the age had been set at 21. In 1928, though, the year of its publication, all women over 21 finally won the vote on equal terms with men. But education for women remained a problem. Higher education especially so. Cambridge refused to confer degrees on women, and the two Cambridge colleges for women, Newnham and Girton, founded and funded by women, could offer tuition but not degrees. Until 1948 the best a woman could expect was a degree in title only – a titular degree, called, inevitably, by those witty Cambridge men, BA (Tit). Thanks guys, good joke.

Orlando has sometimes been dismissed as a romp. This is to misread it. Its gender politics were way ahead of their time

Less than a fortnight after the publication of Orlando, Woolf went to Girton to deliver the second of her two lectures, entitled Women and Fiction. A week earlier she had been at Newnham. Woolf reworked her lectures into her splendid polemic A Room of One’s Own published in 1929. She included the details of two starkly contrasting experiences: an opulent lunch at King’s College with some of her men friends, followed by a threadbare dinner at Girton. She wrote in her diary: “Starved but valiant young women … Why should all the splendour, all the luxury of life be lavished on the Julians and the Francises and none on the (Elsie) Phares and the (Margaret) Thomases?” Woolf was preoccupied by the social and economic differences between the sexes – differences, she believed, that were gender biases masquerading as facts of life. Orlando had paved the way for this more serious and disturbing exploration. The protagonist spends hundreds of years trying to reclaim his own property and cash, legally sequestered after he wakes up as a woman.

In A Room of One’s Own, Woolf asks the reader to consider the following questions: why did men drink wine and women water? Why was one sex so prosperous and the other so poor? What effect has poverty on fiction? On poetry? What conditions are necessary for the creation of a work of art? She had already asked these questions in Orlando.

Orlando is a poet – perhaps not a very good one – but as a man even a mediocre writer is taken seriously. Even the best women struggle to be noticed. But we must keep writing, she told the young women at Cambridge, for in 100 years, and with a room of her own and money of her own, there will be no more gender-imposed limits to a woman’s capacity, or to her creativity.

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Orlando has sometimes been dismissed as a romp. As a less important book than Mrs Dalloway or To the Lighthouse. This is to misread it. It was far ahead of its time in terms of gender politics and gender progress. Consider it not only as the first trans novel in English but in the light of another 1928 publication: The Well of Loneliness.

Radclyffe Hall, who liked to be known as John, was a rigid lesbian who believed that women who loved women were born in the wrong body. This condemned all lesbians to eternal suffering. Her novel was like a depressing version of Orlando. The writing style is terrible – I’d say if you don’t believe me, see for yourself, but that would mean actually reading the thing. Following the sexologist Havelock Ellis, Hall calls lesbians “inverts”. Carol Ann Duffy told me that when she first read this she thought it meant lesbians had sex upside down.

The novel was banned in the UK and there was a court case. Woolf agreed to testify, in the interests of free speech and against censorship, but fretted at the thought of having to say The Well of Loneliness was a work of literature. She was right to fret; it isn’t.

Two novels. Same year. Controversial subject matter. What happened? Woolf, because she can write, because she can charm, because she is funny, perhaps because she was in love, and her style flies along with such ease and grace, managed to smuggle past the censors and the guardians of propriety the most outrageous contraband – a hero who becomes a heroine, who loves women and men, who rails against the system, and whose experiences reflect those of a real-life woman who had numerous same-sex affairs and who went to the opera with slicked back hair wearing evening dress. The Well of Loneliness reinforces every depressing stereotype about gender and sexual desire. It was banned. Orlando exploded all the stereotypes – and became a bestseller.

Woolf, because she can write, smuggled past the censors and the ​guardians of propriety the most outrageous contraband

Orlando smashed up literary categories. Woolf called it a biography – in fact it is a novel. This was a direct hit at her dead father, Sir Leslie Stephen, the Victorian patriarch who had been the editor of the Dictionary of National Biography, a dead white male heterosexual enterprise. Women hardly existed in the DNB. Woolf’s father was one of the senior figures wiping out women from history. And claiming truth. Now Woolf struck back. She started the postmodernist fashion for mixing up fact and fiction, history and invention. We’re used to it now. She’s our pioneer.

When Woolf chases Orlando through continents of history and geographies of time, she is giving herself the freedom to explore the different ages of England, and the changing role of women.

“Did you feel a sort of tug, tug, as if your neck was being broken on Saturday last at five minutes to one?” Woolf wrote to Sackville-West, as she finished the book on 20 March 1928. Woolf, of course, dedicated the book to her and sent her a copy on publication day, 11 October 1928. The love affair was nearly over by then. It had lasted three years, beginning at Christmas 1925, and Sackville-West had altered Woolf’s mind. The author had used every ounce of the affair to propel her own writing, and to alter how fiction could be written – and, in A Room of One’s Own, to discuss how women might soon alter the world with their writing. Not bad, for what she called “a little book.”