A few months ago a proof copy of Sean Thomas’s new book, Millions of Women are Waiting to Meet You, landed on my doormat. I flicked through it over breakfast. A few pages in, I cancelled my entire working day to read it in one go. I had just come to this bit about his first sexual experience as a child: “The first thing I had an orgasm over was the cleaning woman . . . I am weird, terminally peculiar.”

The book is ostensibly about that revolutionary and now ubiquitous phenomenon of online dating, but it is also a sexual memoir, a deft first-person account of 42-year-old Thomas’s entire sex life, warts and all. Thomas loses himself in online porn for days on end: “This is compelling stuff. So compelling I think I’m going to do exactly the same tomorrow. And maybe the day after that I’ll do the same. And the week after that. Indeed the next time I do this, I might stay up for 24 hours at a stretch; after all, who needs sleep when there are people having live group sex in Ontario?”

He is fairly brutal in his assessments of the women he meets: “Her life seems slightly tragic and she appears to be a little mixed-up, but she’s got a Pulitzer prize-winning bottom.” His opinions about women and sex generally verge on the outré: “To this day I find short skirts and gingham dresses very exciting. I also like girls with bare legs.” And he is alarmingly frank on the question of not having sex for a while: “Once, during my schlep across the Sinai of celibacy, I caught myself looking at a ‘naked’ mannequin in a shop window. With lust.”

All of this makes his book compulsive; it is eye-poppingly candid about both sexual successes and crushing failures (Thomas is not of the delusional “I’m so hot it hurts” school), and it is also very funny, even if the laughter is often of the horrified variety. Here, for instance, describing a date who is having difficulty understanding Queen, The Musical:

“The woman is a moron. She is a cretin. She is, I fear, emblematic; in other words, she is crystallising a question that has been locked in the attic of my mind for some time. Just why are so many women so thick?”

I doubt my laughter would be appalled if I were a man — I’d probably be whooping with recognition. But I suppose I find all this rather grim because I am a woman who likes to imagine that men are evolved, sensitive creatures who don’t have sex on the brain 24 hours a day; and I am horrified because I also recognise that Thomas is a kind of Everyman, and that a lot of what he says about women — or rather about what men think about women — is probably true, particularly the bit about sex on the brain or about the way men judge women instantly (of yet another date, who doesn’t look much like her online picture and who puts this down to changing her hairstyle: “I felt like replying: and your dress size? And your beard-shaving regime?”)

His book won’t delight the sisterhood but as a portrait of modern masculinity in a time of crisis, it is hard to fault.

If I were a man, I’d be delighted that someone has finally had the courage to say, “This is how we are. You don’t have to like it, but it’s true and we’re okay with it.” As a woman, I am agog: reading Thomas’s book is like rootling around the brain of some random nice-seeming bloke: it’s fascinating, startling and not entirely comfortable. “I have often found that the most successful, affluent and dominant women (in terms of career) often turn out to be the most feminine and yielding when they get the chance.”

The book is also oddly moving. Thomas writes from the heart as well as from the groin and, crucially, his voice is likable.

So I’m sitting in a London club waiting for him, thinking how weird it is that I know so much about his intimate life. I know, for instance, that if — God forbid — this were a date that we had arranged on the internet, I would be automatically disqualified on grounds of my height, because he likes only short girls (“I prefer short girls. I just do. Short, petite, feminine, sit-on-my-lap girls”).

I know he likes spanking and mild bondage. I know how many threesomes he’s had. I know he’s spent so much time looking at internet porn that he eventually had to wean himself off, like an addict — and I know that when he confesses to this, which he jauntily does, he is speaking for millions of men, one of whom may be living in your house. Of women’s online profiles when they do internet dating, I know that Thomas believes that “curvy” means “ tubby”, “cuddly” means “huge”, “a cat lover” means “desperate for kids” and “scatty” means “bonkers”. Not PC, indeed, but probably true.

I start by asking him what possessed him to be quite so candid. For writers of confessional journalism — Thomas has written a great deal of it, as well as three novels — the trick has always been to conceal as much as you appear to be giving away. Was he concerned about exposing himself so fearlessly? “Um . . . slightly. I wanted to be as truthful as it’s possible to be.” (There is one glaring omission in Thomas’s ultra-honest book: he makes no mention of the fact that he was acquitted of date rape in 1988. “I thought very hard about whether to include that. But I’d written about it ad nauseam and I thought it would really unbalance the book, like putting a brick on a silver tea-tray.”)

Aside from this considered omission, Thomas is not shy about chronicling the minutiae of his sex life. “I read The Sexual Life of Catherine M a couple of years ago and thought it was a very impressive book. I was inspired by it.” But it was written by a woman, I say: explicit sex is a subject on which male writers of non-fiction have traditionally been quite coy (unlike their novelist counterparts). “We’re getting less coy. There’s been a huge change in male sensibility over the past 30 years. And there’s feminism: women have required more emotional input from men and that’s a good thing.”