Four and a half years sounds like a long time to keep a secret – especially a sexual one. Yet last month saw the publication by Orion of the third book under the pseudonym "Belle de Jour". The true name of the former London "escort", cult blogger and then bestselling author remains as much of a mystery as in spring 2004.

Then, every columnist hazarded a wild guess at the identity of the well-read graduate whore (her preferred term) behind the mask. No longer presented as a journal of actual encounters, Playing the Game carries the simple rubric: "a novel". Its creator keeps up the claims to verisimilitude that have helped sell more than 350,000 UK copies of two books about the "intimate adventures of a London call-girl". She invites readers to treat this first-person fiction about a former sex worker's mixed fortunes in civvy street as "a parallel universe for Belle and her mates". Then, in an email interview with Mark Lawson for Radio 4's Front Row, she changed her position once again to assert that "about 75 per cent of the new book is also true". Talk about having it all ways.

Starting in that remote era when newspapers not only had to gloss (or gloss over) Belle's more specialised services but also explain what a "web-log" or "blog" might be, the who-is-she? speculation thrust a stadium-full of improbable candidates into the limelight. Could Belle be Mil Millington, the columnist and novelist who apparently eased her passage into the company of loyal and tight-lipped agent Patrick Walsh, and publisher Helen Garnons-Williams? Or the historian Lisa Hilton – or the novelist Sarah Champion – or punk-fiction provocateur Stewart Home – or the louche literatteur Christopher Hart – or the upscale chick-lit queen Isabel Wolff – or even the ubiquitous editrice Rowan Pelling and all the (now retired) gang at The Erotic Review. The line, to adapt Macbeth, stretched out at least until the crack of doom. But "none of the above" would seem to be the safest answer.

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The fingered contenders for possession of Belle's lingerie wardrobe duly said their piece, and the media caravan rolled on. That journal of record The Times consulted an American "literary detective" who read the stylistic runes and then felt the collar of proud Mancunian Sarah Champion. Over two pages, as Champion later wrote, The Thunderer falsely told its readers that "I was either a fraud or a whore". On the contrary: "Far from a predilection for manicures, Gucci and French affectations, many will testify to my dedication to trainers, pints and northern slang." Stewart Home, the mischief-making Irvine Welsh of Hackney, and a rather more credible candidate for the role of Belle's progenitor, spoke for many critics of the cult. He asked "why the chattering classes prefer fixating on the identity of a latter-day 'Happy Hooker' to examining the economic realities that force many women into this 'profession'?".

The frantic quest to "unmask" Belle as some well-connected jester in Soho or Bloomsbury told us a lot about the mindset of the media types who joined the hunt. They all assumed that any author who quoted so freely and fluently from classic fiction, and commanded such a sophisticated blend of irony, empathy and rather elegant smut, must surely boast a more respectable career (as a hedge-fund broker, derivatives trader or chairman of a high-street bank, perhaps?) than turning well-remunerated tricks for the middle-aged refugees from hearth and home or hyperactive young guns on the make whom she wrote about so shrewdly. I don't suppose that gossip writers read much Maya Angelou, but in the second volume of her autobiography – Gather Together In My Name – that feminist icon explains that she fell in love with Dostoyevsky and the Russian classics just as she drifted for a while into casual prostitution in California. One of Belle's posts invites us to reflect on the great medieval philosopher and "Think of Occam's razor: the principle of parsimony. What would be simpler – that I am who I say I am, or that I am a famous author living a double life?".

I knew that Belle was the real thing (in one respect) when I asked her to choose a favourite book for The Independent's "Book of a Lifetime" column just as the first book of the blog – The Intimate Adventures of a London Call-Girl – appeared in autumn 2005. She emailed one, perfectly sound piece about a set-text English classic. Then she decided to replace it with another: a tribute to Stendhal's landmark novel of cocksure male adventuring, Le Rouge et le Noir, and its hero Julien Sorel: "not a transparent collection of ideologies, not a symbol, but a real, breathing human". These read like the second thoughts of a proper writer, not a collective PR stunt. Even if Belle were to be unveiled today as a senior publishing editor from Camberwell who cackled into her New Zealand sauvignon as, thanks to this lucrative persona, she booked the family into a Renaissance villa in Tuscany rather than a camp-site in Brittany, that judgement would still stand.

The hooker-or-hoaxer? squabble will rumble pointlessly on. Liz Miller of the literary website Bookslut points out that the blog has continued far beyond the escort-agency stint that spawned it. Since (thanks to dramatist Lucy Prebble) Belle morphed into Billie Piper for the ITV2 adaptations, she can now comment in pure postmodern vein on her telly incarnation. Mostly, she approves. For Miller, this long afterlife hints at authenticity: "I can see someone faking the blog of a prostitute – but the blog of an ex-prostitute? There have to be better ways to spend your time."

But authenticity is never the whole point – neither in commercial sex, which must always be a masquerade, nor in the very long tradition of spinning yarns about it. Belle belongs in genre of sell-and-tell confessions – genuine, faked or intriguingly in-between – that date back at least to the lubricious literature of the early Roman Empire. Of course, literary genres follow their own arbitrary rules – just like Belle's own artfully stage-managed episodes. Readers will know, as she plainly does, about the grim street-level data of addiction, abuse, exploitation and – at the very worst – human trafficking, all festering far below her deftly lined and shadowed eyes. You might argue that the polished escapades of Inspector Morse and Commander Bond have little obvious connection with the squalid and wearying grind of detective and intelligence routines, either.

But Belle's skill in remodelling an existing genre proves nothing one way or another about her previous career. As she correctly notes, "My books are mass-market... Which means, in a nutshell, they're edited. I have an editor (formerly the Fabulous Helen [Garnons-Williams], now the fabulous Genevieve [Pegg]) and a copy editor whose tasks are to make certain not only that each 'I' is dotted and 't' crossed, but also that the content is comprehensible to my audience – which, judging from the feedback, is a very general one." All mainstream writers, whatever the autobiographical percentage of their output, nip and tuck their tale to suit a chosen convention. This is the dark truth about that flogging of collective fantasy that goes by the name of popular publishing.

So the single thing we know for sure about Belle is that she is a real writer. Alas, Playing the Game begins to disappoint on this score. Overt fiction sends her too far down the chick-lit, bad-dates road, and threatens to dumb down her peerlessly piquant voice. In the novel, her fictional alter ego – or alter-alter ego, perhaps – attempts the nine-to-five: "a civilian now, like everyone else". Predictably, she loathes office trivia and – after moving in and splitting up with on-off paramour "the Boy" – considers the option of a timeworn halfway house between straight work and sex work: as kept mistress to a wealthy "Silver Fox".

The plot, however, tiptoes down Banality Boulevard, with far too much standard-issue single-versus-hitched introspection, a succession of nightmare almost-boyfriends, and a trouble-at-work sub-plot that's annoyingly vague about the business involved. The bracing clarity of her orifice politics does not extend to office politics. Here, her talent and attention sometimes seem otherwise engaged. So one hangs on for the sporadic orgasm of the Belle epigram, as when she massages TS Eliot's "Cruellest month" into a harder form: "April, herpes, and Cliff Richard: like it or not, they always find a way back."

One can still read this ex-call girl's fabrication simply for its by-blows of literary criticism and allusion. She scatters opprobrium over the oeuvres of Leon Uris, Terry Pratchett, Patrick O'Brian and even (I'm afraid) Paul Auster. Her cultural heroes include the much-missed Scottish maverick poet-performer Ivor Cutler. Now, who would bother to make that detail up to fit a fictitious retired harlot? Well, I suppose, Stewart Home might. On page 71, by the way, Belle quotes Philip Larkin's "Dockery and Son" without attributing the lines. And she avoids the cliché citation from that poem: "Life is first boredom, then fear." Pure class.

Larkin's presence signals that solitude as much as sex propels these books. (Incidentally, does Belle know that in his lustful but tormented youth the poet penned salacious girls'-school novellas under the draggy pseudonym of "Brunette Coleman"? I hope so; she'd enjoy them.) In the saddest passage of Playing the Game, Belle's prickly disbelief in any lasting togetherness picks up an almost existential heft: "you arrive alone; you leave alone and soul mates and all that crap be damned. Inside your head you live alone."

Against that abyss of solitude, Belle relishes the passing company of her tricks. She comes across as a comrade; a fellow-soldier in the battle of life. She mocks women's glossy magazines, deeply bored by media-dictated girly topics despite the professional armoury of scanties, frocks and maquillage she has to command. Her clients arrive as confused tourists from "the world of reason" where they rule, wounded by the other domain of feelings that seems "as foreign as a franc". She does what she can to help: "I liked these men. I understood these men. They were my people." One of the less obvious attractions of these books is that they voice a curious longing for male-female solidarity (not the same as intimacy, of course) at a time when Mars-versus-Venus platitudes about the unbridgeable gulf between the sexes flood mass-market culture. In print, Belle does post-coital camaraderie almost better than anything that comes before.

When the first Adventures proved not merely a succès de scandale but a palpable chart hit, Belle bred a host of horizontal wannabes. Inside a few months, a dozen publishers seemed to have picked up their house tart, supposedly real or frankly fictional. However close or distant their relationship with truth, the "memoirs" of the madam, the mistress or the minx became a must-have accessory for every ambitious list. Inevitably, most of these books sucked (so to speak).

Still, that tide of tart-lit proved that periods of rising, unequally divided wealth, social upheaval and moral perplexities in fast-moving cities tend to nurture a lively literature of prostitution. From the first-century Rome of Juvenal and Suetonius to the Georgian London of John Cleland's "memoirs of a woman of pleasure", Fanny Hill, to the Second Empire Paris of Dumas and Baudelaire, the fate of harlots high and low have shocked or stimulated readers who thrill to murky deeds in the wicked metropolis.

In English literature, the parade begins in earnest in 1722, with Daniel Defoe's Moll Flanders: "12 year a whore, five times a wife... 12 year a thief", but who "at last grew rich, liv'd honest and died a penitent". With the claim that Moll's life was "written from her own memorandums", Defoe pioneered the marketing of the working girl's confessions as documentary realism. So common did the device of a male author ventriloquising the memoirs of a smart tart become (Home tried it himself in Down and Out in Shoreditch and Hoxton) that Belle, of course, looked like the latest episode in this centuries-long serial.

Whether battle-hardened businesswoman (the Fanny Hill model) or tragic victim of hypocrisy (Romantic-era Traviatas), the literary whore has always had to mirror the urban vices of her time. Typically (and here Belle plays the traditional game with her sincere insistence on total insincerity), these involve a surrender of solid verities to the superficial allure of the facade and the performance. In an era when anything goes, a glimpse of stocking – or basque, or thong – never hides a deeper reality. What you see is all you get.

In such literature, the prostitute tells a truth about her glossy, glassy time that echoes far beyond the discreet bordello doors. Etymologically, the word "meretricious" means "whorish", after all. In any society of gaudy spectacles, the figure of the sex-seller will have a starring role. So, as a deluded London decade of high-financial trickery, gravity-defying debt, snake-oil and spin crashes to its end, we should probably be glad the bedroom professional who marked its zenith should have had so much wit (and not a little heart) about her. If Belle had not – in some form – existed, then the age of leveraged buy-outs, credit default swaps and self-certified mortgages would have had to invent her. But then, perhaps, it did.