Deviant lifestyles in fragrant surroundings are always a bit of a shock. One afternoon I knock on the door of a Victorian semi in a desirable street in north London, average house price £700,000, all period features and private schools. A middle-aged sex maniac answers the door; she is the author of graphic, no-holes-barred (sorry) erotic memoirs and she looks frankly disappointing. Not a love bite or a stocking top in sight. Instead a long, flowing skirt, subtle make-up, curly blonde hair strictly tamed, and covered for our pictures with a dark wig. The only giveaway (but not really) is a low-cut top from which breasts – for which she receives the gratitude of many – threaten to spill. Does she have a parking voucher, please?

I wonder if “Dr Donny”, the tall, dark, handsome stranger who arrived on this very doorstep one morning, interrupted the flow of their shared fantasy to satisfy local parking regulations. Probably not. The wardens are hot in these parts, but not as hot as the sex. Their assignation was arranged via a chatroom and telephone call: she opened the door and ran upstairs, while the “doctor”, actually a fund manager with a stethoscope and an unusual bedside manner, followed on. He could have left her robbed and battered – though rape would have been a pretty impossible charge to uphold – but instead he left his calling card and asked to come again. This is the woman men have always believed exists, the saucy nympho who beckons from her door with a smile and a negligee, the one their wives insist is a figment of their fetid imaginations. This woman is a reward for their unfailing hopefulness. She is also their worst nightmare: a merciless judge of male members.

Portnoy has written two books, in the tradition of Anaïs Nin and Catherine Millet, though thankfully she has none of the latter’s literary pretensions. The first book, The Butcher, the Baker, the Candlestick Maker, was published two years ago to a gratifyingly outraged response (the Daily Mail painted her as tragic, which, for a self-appointed iconoclast, is pretty much the Oscar). It sold 30,000 copies in three languages, very decent figures for her genre. As far as she can tell, her readers are fortysomething women whose partners read the books rather than buy them.

She is in successful company: titles such as Jane Juska’s A Round-Heeled Woman and Abby Lee’s Girl with a One Track Mind have turned erotic memoirs into breakthrough blockbusters. Portnoy’s follow-up, The Not So Invisible Woman, is published this month, not so much a sequel as more of the same. (Her editor at Virgin Books said not to worry; more of the same would be fine.) She also runs a blog, which she launched to market the books, with a podcast dispensing master classes in bedroom events.

She is rather like Delia waxing about the variations on a classic victoria sponge, full of helpful hints on technique and tips for foolproof results. Isn’t she embarrassed? She laughs, putting her head on one side, all cutesy. “Aw, no, I like it too much.” Her books are a rampant picaresque through naturist saunas, swingers’ clubs, fetish joints and online chat rooms where chat is the last thing on the agenda; pornographic and crude, the smells and emissions of copulation are their obsession. If you took away the dirty stuff, no narrative would be left; if you took away the internet, there would be no Portnoy persona at all. Cybersex and its global confluence of niche peccadilloes rescued her life – or ruined it, if you are a moralist – from the sexless invisibility of the middle-aged woman, described and sometimes welcomed by feminist writers such as Germaine Greer, but not by a gal who wants to make trousers strain at the seams.

We have spoken before, Suzanne Portnoy and I. In her straight life, using her real name, she is an entertainment PR with whom I once tried to set up a story. It didn’t work out, but she offered me tickets to a family show she thought my little son might enjoy: friendly, professional, to the point. This is clearly how she runs her sex life. As I walk into her kitchen, she points out the hot tub in her small back garden, first stop for the conquests she brings home (second stop: kitchen table); it is overlooked by an entire block of neighbours, which amuses the new heroine of clit-lit.

Portnoy, 46, is straight-talking, shameless. She laughs all the time, a big, brash, pearly toothed laugh, which is her weapon and her armour; she acts brazen, but actually she is trying to stop you getting to know her. When you have sacrificed your sexual privacy, you guard your domestic trivia, the only secret left, like a rottweiler.

Having read her books, you know more than you could ever want to know about a divorced mother who doesn’t wear knickers: you know what she keeps in her bedside cabinets – and it’s not Vicks Sinex nasal spray like me. Her ideal weekend, when her two sons stay with their father, is as a single woman on the swingers’ scene.

Portnoy was married to a handsome executive in the entertainment industry for a decade. It was a rocky marriage, latterly celibate, which set her on the road to sexual nirvana. “Suzy housewife” was overweight, frustrated, subsumed in home-making and motherhood. The sex, which had never been explosive, became a distant memory. “I suggested to my husband that if he wanted to kick-start our relationship he should buy some porn. He just said, ‘You’re sick.’ My kids were always wrapped around me. I couldn’t bear anyone else to touch me.”

One night when she was drunk and her husband away on business, she meandered online to a contact website, insisting that all she wanted was a male pen pal with whom to discuss her life. Instead she met a New York lawyer with whom she shared a sexual epiphany. She flew to see him for sex, at first lying to her seemingly unconcerned husband, once – and this is where I can’t help disapproving – even taking her young kids to stay in his flat while his own family were away. “We were catalysts for each other’s sort of sexual journey,” she recalls in her twangy hybrid transatlantic accent. “He wanted to explore sexual experiences. And I felt as if I was going back to my twenties and reinventing myself.

It was very exciting and scary. There was a lot of fantasy. I love fantasy.” But with Portnoy it doesn’t remain fantasy for long. The only thing he wanted that she couldn’t provide was to be told how much she hated him. Her fellow travellers, you see, are not just hedonistic pioneers: the damaged are present in numbers. The self-destructive are happy to be selling themselves cheap; the addicts are seeking oblivion. Curiously, however, none of this is the case with Portnoy.

The daughter of conventional and happily married parents in a close-knit Jewish family, she was a bookish girl, growing up in London and America. They gave her little to rebel against, if that’s what we were assuming; a liberalism she has bestowed on her own sons, aged 13 and 16. “My children are so straight that it’s funny. My youngest son said to me once, ‘You tell us we can do anything, we can talk to you about anything, but because you’ve done it all, we don’t want to.’” She warns her older son, but gently. “I say, if you are gonna have sex, please be safe. If you’re gonna take drugs, don’t take a lot of them.”

Is Portnoy safe herself? In seven years of wild sex with strangers she can only recall one incident that looked as if it might turn nasty. Paradoxically for a secret life, she sticks to public places; she is regularly tested for diseases she has never caught; she uses condoms. Even when blindfolded in a sex club, the only thing she demands is that male members be properly dressed.

She lost her virginity at 17, was sexually adventurous at university, was made miserable by unrequited crushes in her twenties. She has more than made up for that in middle age by casting a smaller net and turning an ocean of unavailable men into a pond of appreciative specialists. In the real world she might find it hard to hook a handsome banker; she’s too old, too curvaceous and, as she herself says, “hardly Cindy Crawford”, probably too loud and scary to boot. Being single at swingers’ parties, however, makes her hot property; being adventurous makes her a catch; truly enjoying sex makes it all easy for her.

But not as easy as the internet makes it. With a ready-made infrastructure of infidelity, women can advertise for NSA (no strings attached) encounters. No longer needing to brave bars and clubs to meet men, straight or swinging women access hook-up sites such as or, along with texts, webcams, hidden e-mail accounts. Portnoy’s favourite, Swinging Heaven, boasts over 800,000 members, mostly men; but look out, boys, she says, the women are coming. Memoirs like hers are the glossy brochures for a libidinous minibreak: the books are leading the curious to experiment, the sex is producing the books, and growing the market. Her editor at Virgin Books, Adam Nevill, talks of a “sexual revolution… not dissimilar to what happened in the Sixties in terms of changing attitudes to sexual lifestyles”.

The writing started while she was living with a boyfriend, Daniel. She sent his unpublished novel and her cheeky blog, detailing her life as a London PR, to a publisher, who asked her to turn it into a book. Tragically, Daniel died of liver cancer. I’ve never read a more perfunctory description of the death of a lover; but then she keeps the stuff that makes her cry to herself – she will open her legs to a roomful of men, but she won’t open her heart. Though she no longer loved him, she tried to score some Viagra so that she could make his last weeks more tolerable. His doctor was appalled, but you can’t help admiring her courage in making the request. By the time she got the prescription, he was too sick for sex.

His death in 2005 was the launch pad for her dive into sexual adventure, as if every day were her last. While he had been dying at home she had found solace by logging onto a swinging site. The day he passed away she went to Rio’s, a unisex naturist club in Kentish Town, where brushing a thigh in the sauna or a fumble in the Jacuzzi (whose waters you’d think twice about sampling) can soon spark a mini-orgy in a specially allocated room. (The place is mentioned so often, its owners should sponsor her website.)

“I thought, I really am going to have a good time now. I’m gonna go for it in a major, major way. And a friend of mine who had suffered the death of both parents in a short period of time told me she’d have shagged a tree on the day her mum died. I felt like that. It’s like sex is an answer to death, grief and everything. You just feel like, ‘Give me something that makes me feel alive.’ ”

In the middle of this maelstrom, she met 50-year-old Greg, her long-time swinging partner and sexual mentor, with whom she now shares a cosy if unusual Memory Lane. A year or so after Daniel’s death, with six boyfriends on the go, she started to write her adventures, unencumbered by modesty, euphemism or guilt.

Is there something wrong with this woman? In the past her friends have worried about her, begged her to get help for sex addiction. And a Freudian analyst could have a field day with her insatiable need to be “filled up”; what is it that makes her feel so empty? Her lifestyle has lost her friends: judgmental women, mainly, those scared she would steal their men, and, I imagine, those who just thought it was all too seedy. In general, women need their friends to affirm their own life choices. Portnoy’s are too outré for comfort, too strident to be challenged, begging too many questions she can’t or won’t address.

We are roughly the same vintage, mothers of boys, writers, I am married, monogamous (sexually comatose compared to Portnoy). We have much and nothing in common. The longer I spend with Madam Sin discussing the etiquette of sauna sex, as sweet children gaze from framed school photographs on the shelf behind the sofa, the more I become aware that my life would horrify her, just as hers terrifies me. Liberation?

I cannot imagine anything worse than texting around London for men willing to stage a gangbang. To be honest, even the idea of maintaining an ever-ready bikini line is too much. Actually, to be really honest, the late nights would make it a deal-breaker. Is she a bad woman as well as a very naughty girl? I don’t think so. There is nothing wilfully cruel, or negligent, in how she treats others, but grading men according to the size of their penises seems a pointless reversal of the old sexism we all marched and shouted about a lifetime ago.

If she is impressed with the equipment, its owner might be admitted into her stable of studs, her rotating “dating portfolios”. Sexy Suze travels like a surveyor with a tape measure. Numbers present more of a problem than size: she can’t tell you how many men there have been because she stopped counting at 100. And for all her claims about being “in control”, isn’t she turning herself into a commodity to be used? Her answer is: as long as she’s enjoying it, so what? The censorious voices of Catharine MacKinnon and Andrea Dworkin might say that her voraciousness is feeding an industry in which women are base material, the pole dancers and strippers, the hostesses and lap-grinders, who are economically if not physically abused. The UK cyberporn market, to which she subscribes, was the fastest-growing in the world in 2006, its profits soaring into billions, many of its addicted victims trailing broken relationships behind them.

Why doesn’t she have a boyfriend? After her divorce she dated with a view to finding a replacement, but she stopped on realising that she already had one – or, rather, several. She looks at men practically: can they outwit her boredom threshold, match her schedule? “People say that love can conquer all. That’s rubbish. When you’re 47 you’re sorted, you’ve got your life. I meet twentysomething girls who think they’re sexually liberated, but the bottom line is that they’re trapped in a Cinderella fantasy, desperate to meet Mr Right, and thinking that the baby is gonna make it all perfect. It’s a generation thing. I was just the same.”

She calls herself a polyamorist, and is still looking for the primary relationship around which her more casual affairs – all long-term and ongoing – would cluster. Her psychic advises that she stop dismissing men as boyfriends for their tiny flaws; she has just got rid of one because she couldn’t deal with his teeth. What did for the New York lawyer was his dingy apartment (she’s a design snob) and the fact that he served her pasta on paper plates.

What are the logistics of running a double life? Actually, despite the pseudonym, disguised photographs and the avoidance of television, her cover is so flimsy it has been blown (or given away) many times. Her pen name (also a reference to the sexually ground-breaking Philip Roth novel) is less of a disguise than it would be if she really cared about anonymity. Her PR clients are apparently unperturbed. “To be honest, it’s pretty common knowledge who I am,” she says. “A lot of my clients know. In the area I work in, people are taking drugs and doing all sorts of shit. I sleep with a few people – so what? I’m not a police woman or a teacher.” Yet she appeals to you to be careful in protecting her identity, and clearly frets about it, which must be exhausting. She describes her life as “compartmentalised”, but the danger of crossover is constant; actually, she is trapped between proving that she is not ashamed of her sex life, and wanting to protect her sons. “They’re at an age where their friends might, you know, tease them.” Tease them? She works in the media, which employs many of their schoolfriends’ parents, and if her indiscretions ever reached the playground, it would be a case of torturing them rather than teasing them.

At first she seems to be saying that she hides her exploits from them. But the family computer is her cybersex club. And haven’t they found copies of her books lying around? “Oh, sure,” she laughs (and the laugh is definitely strategic), “but they’re not interested in my writing. It’s a bit like reading your mum’s diary.” Yes, I agree, and I would have ploughed through my own mother’s secret garden in two minutes, amazed and appalled. She shrugs. “They say, ‘We don’t want to know. Just as long as we don’t come home and you’re in an embarrassing situation.’” While we are talking her older son returns; tall, polite, saying hello and dashing upstairs, aware that I am “the journalist”. Why has his mum shared her predilections with a prurient or disapproving world? Not just for the money (her advance for her first book was “a couple of thousand”, though for her second the figure shot up to £20,000). She is an attention-seeker for sure, but it’s mainly because she sees her behaviour as meaningful.

“I can be a figurehead for a new kind of female sexuality,” she says seriously. She tells her kids that people are comforted (of all reactions to her prose, that must be the most unlikely) by her work. “My readers are relieved to hear that being sexual in your forties doesn’t make you a freak.”

If her sons asked her to stop, would she? She hesitates. “I think that… that’s a difficult… I don’t know. Obviously I want to protect them, but the bottom line is that somebody has to do this, and I’m the one who’s been chosen. It’s really important to me. They know that.”

I wonder what private conversations her parents might have about their beloved daughter’s antics, and their concerns for their grandchildren. I don’t imagine Portnoy gives it a moment’s thought. There is a selfishness to her quest, maybe partly the righteous urge to liberate a generation, but essentially focused on sating a mighty libido and bolstering an ego that is not as robust as we might assume.

Portnoy is an evangelist. She recommends her lifestyle to all. If most couples’ sex lives wither for want of communication, her scene is all about instant honesty. “It’s like the first-date conversation is, ‘Okay, if you could do anything, what would you do?’” When she reads those surveys about women preferring chocolate or shoes to sex, she assumes they must be having bad sex. You can see that it works for her. I don’t suspect her of exaggerating her exploits, or of lying about how happy they make her. Here is one menopause-bound woman at least who doesn’t grimace every time she passes a mirror, who may have found the alternative to HRT and acupuncture: so much sex that her serotonin levels keep her zinging as the oestrogen plummets, so many compliments that she is enviably convinced of her gorgeousness. “I’m constantly validated, so that’s how I see myself.” Will she be too old one day? A friend in her mid-fifties has suggested stopping at 85, and Portnoy seems satisfied with that.

Recently the action has slowed. After a course on tantric sex, she was counselled by her instructor to stop chasing orgasms and re-engage with the intimacy of sex. “I’d gone so much into fantasy and role-playing and swinging that I couldn’t just be with somebody and enjoy that.”

She has a handful of regulars, a “breakfast thing”, once every six weeks. She wants to make her Portnoy persona a full-time job, with a late-night-radio agony-aunt slot, a cross between Dr Ruth and Linda Lovelace, part of her qualification for which is that she loves men. “I never think of them as bastards,” she says benignly, but then she never allows herself to be let down by them. A producer friend of hers is chasing the film rights to her books, though quite how you’d make them more than a porno flick is hard to see. Being a published author has made her a celebrity at her old haunts and garnered a fan base (and some hate mail too). She admits that she could have her pick of her fans, but actually doesn’t take the opportunity. Her female correspondents seek advice on initiation into more and better sex; 80% of her letters are from men wanting it with her. She may fear intrusion, but I think she loves the power over men, normally only accorded to the super-beautiful, the youthful, the alluringly and unavailably sexy. When a fan asked her to lunch recently, she agreed on condition that he bring a gift of her favourite lingerie in her size; reading between the lines, she felt his disappointment that, despite her careful grooming and twice-a-week personal trainer, she didn’t look more like a fantasy creature. Tough. She doesn’t dwell on the knocks.

Portnoy is bold, self-assertive, but maybe a little disingenuous about what she wants from men. It is not quite as simple as just sex, nor as complicated as true love. She wants to be treated, pampered, showered with the perks enjoyed by wives and mistresses; she wants top trips, dinners – all the tokens of romantic esteem. Of course she “dates” penniless super-studs, but those who can’t perform for their supper might be expected to buy hers. That doesn’t mean she’s grasping, but that running her own cabaret is tiring, and even the feistiest impresarios need to feel looked-after sometimes. One problem is that, when what you love best about a man is his penis, he’ll probably end up resenting you for the compliment. Especially if you’re keen on rival specimens too. I’ll never read her books again – not my thing – but I’ll always wonder if her lust will see her into a cheerfully ribald old age or leave her stranded.

For all her saucy fan mail, Portnoy wants to be a poster girl more than a mature pin-up, a walking advertisement for unleashed female sexuality. She smashes taboos like glasses at a Jewish wedding (though I can’t see one of those on the horizon) and has tapped into a publishing market churning out the evidence – a sort of frontline sexual reportage, complete with casualties – that no-strings sex is the way forward. For a single woman whose main emotional attachment is to her children, it might provide short-term answers, but how many are there with this one’s industrial appetites and nonchalance about disapproval?

What makes her tick would make many women – even bold, curious, frustrated ones – feel unanchored and confused, ultimately lonely. Recently she met a woman at a party who told Portnoy her book had changed her life: she had begun an affair. Since infidelity is the most commonly cited reason for divorce, maybe she shouldn’t be so quick to congratulate herself on liberating the drearily married.

And what of her own future? She can stave off the loneliness of the empty nest with sex, keep her contacts updated, her publishers supplied with salacious manuscripts, but it might someday become a chore. As the chill wind of mortality rushes up her geriatric miniskirt, wouldn’t she rather be at home with a nice mug of cocoa, a faithful husband, even a cosy pair of knickers?

The Not So Invisible Woman (Virgin Books, £7.99) by Suzanne Portnoy is out this week

Memoirs of sex-seeking women

Frontline sexual reportage is a bestselling genre: 300,000 copies of books like these are bought every year.

Melissa Panarello’s One Hundred Strokes of the Brush Before Bed, based on her own diaries, is the tale of a teenager’s multifarious sex life. Its frankness scandalised Italy; it has sold 2m copies worldwide.

Chick-lit gets ruder in this book by a London-based sex writer who calls herself “part slut, part hopeless romantic”. She sets off on her quest for a soul mate — who must also be a sex god — with comical results.

Catherine Millet, a French art critic and editor, gained instant notoriety with this graphic memoir of gang-bangs and orgies wrapped up in philosophy. Despite its pretensions, it has sold almost 1m copies in Europe.

An opera-loving teacher of English, Juska placed this ad in the New York Review of Books: “Before I turn 67 next March, I would like to have a lot of sex with a man I like”. What ensued became a bestselling memoir.

Women and sex: facts and figures

A number of surveys reveal how important sex is to the British woman, especially if she is over 40

Half of British women are not satisfied with their sex lives

59% of British wives say they would leave their marriage if they could afford to

One in nine British women regards sex as “like any other household chore”

British women are twice as likely to be unfaithful as their French counterparts

40% of women over the age of 40 admit to being unfaithful to their partner

In a survey of fortysomething women, 70% said their sex lives were better than ever before;

82% said sex was as important as it was in their twenties; 45% wanted more sex than ever before; 69% felt more adventurous in bed; 66% felt more confident about their bodies

Almost two out of three British women have logged onto a personals website

Nearly 50,000 women visited the Erotica lifestyle show in west London last year.