Purcell recently outed himself as the reclusive author Natasha Walker, writer of the erotic fiction trilogy, The Secret Lives of Emma, which followed Fifty Shades of Grey into the mainstream.

''A lot of guys I know will stay in the men's section. They'll read their Cormac McCarthy and their Martin Amis and they will return again and again to this cul-de-sac of maledom. But once I crossed over to reading women authors, I never crossed back. The greatest propagandist for moral behaviour is Jane Austen. I fell in love with Fanny Burney, Elizabeth Gaskell and the Brontes, then I found George Eliot - the list goes on.

''I think that's something a lot of male readers have to do, eventually: read more women … they'll become much more interesting people.''

It's something of a turnaround for Purcell who once owned a second-hand bookshop in Mosman. Purcell spent more time reading and writing his own opus than selling books, inevitably to the detriment of his bottom line.

When a customer walked in, he would try to dissuade them from buying the latest John Grisham or James Patterson thriller, substituting some worthier classic: a Dostoevsky, a Hardy or an E.M. Forster. Even Charles Dickens was once too popular for Purcell's highbrow tastes.

From his vantage point across the counter of John's Bookshop, Purcell could easily have been the inspiration for Bernard Black, the grumpy bookseller from the British television series Black Books.

''Yes, that was me,'' the tall man admits gleefully, his face still bearing traces of a mussy-haired introvert. ''I had no interest in business. It was really a place for me to sit and pontificate, and I was completely anti most of the books in the universe. It was just the classics and the greatest writing possible.

''When people weren't reading that, I wasn't interested.''

Who would have thought this literary snob would one day reveal himself as the standard bearer of erotic fiction, that rather friendless genre of commercial women's fiction?

The pseudonym had been Purcell's idea to shield his stepchildren from the adult content, and his own reputation from the chance of ruin. Publisher Random House went along with it, thinking readers would be more comfortable with a woman writing erotic fiction.

Given his early anxieties, Purcell was prepared for the arched eyebrows and an autobiographical reading of the sexual proclivities of his married heroine and her lovers.

The Secret Lives of Emma series has sold more than 50,000 copies and last year made Purcell one of the best-selling debut authors in Australia. As head of marketing for Australian online bookstore Booktopia, Purcell has tracked a further kick in sales since his unmasking.

What he did not predict was the pride and protectiveness he feels for his creation, Emma Benson. Emma's character is based on strong, capable women Purcell has known, his mother and two elder sisters, and ''women who have scared the crap out of me. I know these people exist, I've had them in my life, and they've been demanding people to try to cope with.''

Emma upends the stereotype of women as sexually passive with a libido attuned to monogamy. A year married to her banker husband, an ''insatiable man-beast'' between the sheets, Emma begins the trilogy restive for new sensual pleasures, and spies it in the long-limbed boy next door.

The pairing of Emma, a woman hardwired for promiscuity, and pubescent Jason had not been all Purcell's idea. While it spoke of his own adolescent fantasy of the sexual novice being inducted by an experienced older woman, it had been his female reviewers who urged him to have Emma act as the boy's instructor. Whatever you do, they had warned, ''Don't do the Penthouse thing where [sex] is all over in a few lines.''

Sex, Purcell suggests, is about the only subject of modern life worth writing about because it frightens, bound up as it is in relationships, questions of property and marriage, and an innate sense of right and wrong. Writing good sex, he insists, is more cerebral an undertaking than it might first seem.

He drew inspiration from Henry Miller's graphic realism. Sex was ''grubby and dirty, accidental and awkward'', Purcell says. ''Things fall over; things go crunch. I love that there were all these realistic things that turn up in his sex scenes. He doesn't go all out to describe the parts of the body; he was describing physically what happens but it is all the stuff that goes on inside the lovers' heads that I've tried to use.''

Purcell wrote his first erotic story for the same reason he once became a vegan - to impress a girl, in this case one who had been shown an erotic story by a rival. Egged on by female friends, he wrote ''ridiculously rude'' short stories he thought no one would want to publish and plonked them in his filing cabinet along with his other scribblings, until his agent came asking for a new manuscript.

A week after he handed it over, ''Fifty Shades broke and everyone was scrambling for erotic fiction''. With no time to spare, Purcell tore his manuscript to shreds, moulded it into two story arcs, sketched a third, then wrote like a ''crazy man''.

Among the few to know his secret identity were his wife, Tamsin, the girl he had admired from his storefront window, and new boss Tony Nash, the founder of Booktopia, known for its emphasis on Australian titles and romance.

The Secret Lives of Emma suffered at first from comparisons with Fifty Shades, which in Purcell's assessment is, in essence, a traditional romantic novel. For all ''the dirty stuff that accountants like to do'', Fifty Shades plays it safe with a virgin and a wealthy man as her suitor and sexual instructor, both ending up happily married. Among conservative female readers, Purcell's transgressive plot of infidelity elicited ''shock and horror''.

For all the genre's failings, Purcell struggles to understand why, with the industry facing extinction, Australian publishers are ''moving away from erotica as fast as they can''.

''Australian booksellers and publishers seem to believe that erotica is done and dusted and there is nothing else to be said about it,'' he says. ''Fifty Shadeswent out to 1 million readers, and I'd say 98 per cent of those hadn't been reading anything at all regularly and we let them go. We didn't chase them down.

''The same thing happened after Twilight, the same thing happened after Dan Brown, the same thing happened after The Secret - those big explosions of our market and readership - and we let them go, time and time again.''

Purcell was once an unengaged reader. At a Catholic boys' high school, he was bright but had trouble reading. Then, ''five minutes to the HSC'', a friend lent him a copy of Joseph Heller's Catch-22. It caught his imagination. An English teacher recommended he read E.M. Forster's A Room with a View.

''I dug it. The emotional content was wonderful: the choices the characters made, the moral distinctions they made. Everyone was thinking about everything; nothing was thoughtless. I love that - I've always looked at the world and thought more before committing myself to action. I constantly examine what people are doing to make sense of it all.''

After school, Purcell wandered overseas. ''That was my shouting-at-the-world period,'' he says. Having followed an Italian student of philosophy to Milan, Purcell realised how ignorant he was.

''There was a good reason I got zero in the HSC: I had taken little of what the teachers taught me into my head and I was embarrassed among all my educated European peers.''

Returning home, he spent the next two years reading everything he could. The more he read, the broader his palate. In the bookstore he established with a $10,000 overdraft, he wrote A Gentleman of Sorts, a sprawling historical novel set in a northern English factory town at the turn of the 19th century that he has rewritten and refined for more than a decade. It is with publishers now. ''It's got adventure, romance, betrayal, kidnapping, and there's a murder in the middle of it all,'' Purcell says.

''There's a bit of Hardy, a bit of The Count of Monte Cristo, it's got a bit of Les Miserables and the craziness of the Brontes.'' And, yes, Dickens.

The Secret Lives of Emma trilogy is published by Bantam Australia, $17.95 each.