There's a tragic truism that nobody ever tells a bride-to-be, namely that if a couple puts a pebble in a jar every time they make love in the first year of wedded bliss and then removes a pebble every time they make love thereafter, the jar will never empty.
It's quite a bleak image for a loved-up newly wed (which is why they are, wisely, kept in blissful ignorance) but for those of us with quite a few more miles on the marital clock, those pebbles are an oddly consoling reminder that, once upon a time, we did have sex. Quite a lot of sex, that was both lovely and indeed lively. And then we had children and, as is the natural order of things, their Once Upon a Times became the focus of family life and evenings were less about hearts and candles, and more about Charlie and Lola.
So when I read that married couples have sex, on average, three times every four months, I found myself nodding my head in agreement - until I realised, with horror, that the report said weeks not months. Who are these crazed sexpots? Are they Scandinavian?
Aren't they shattered and strung out by working by day and comforting (and or shouting at) wakeful children by night? Apparently not.
More saliently, do I envy these women and their nymphomanical nocturnal activities every nine calendar days? No! Yes! I'm too tired to think, never mind exfoliate and dab my temples with Chanel No 5.
Children per se aren't the passion killer, no, our sex drives have been decommissioned by the turbo-charged multi-tasking that is modern parenthood.
It's no longer enough to keep the children alive; we have to nurture them and drive them to after-school activities, organise playdates and stop them accessing unsuitable websites and then, when the lights are off, hack into their phones to make sure they're not sexting.
I suspect one reason the new survey reports that couples are far less tolerant of infidelity now is because for many, having the time, the energy, the headspace for languorous sex is such a rare treat, such a fairytale, that the realisation your other half has been selfishly having some on the side is a shocking betrayal on almost every imaginable level.
The trick is to ensure your spouse is as knackered as you are, thereby extinguishing any last batsqueak of testosterone. Only a couple run ragged with kids can truly appreciate how good it feels to swap the hurly-burly of the chaise longue for the deep, deep peace of the marital bed.
Jim White, man's view
I have never been invited to share my sexual experiences with someone with a clipboard - but if I were, I suspect I know my reaction. I would be gripped by the compulsion to exaggerate wildly, to big up the good times, to make a sexual mountain out of a diminishing molehill. After all, I am a man.
Men have traditionally claimed to have had far more partners than women: even today, when the gap is apparently closing, the average bloke is reckoned to have slept with around four more partners than the average woman.
I am prepared to believe that in these days of social media and reduced restrictions, some 16-year-olds enjoy earlier induction to physicality than 40 years ago. For the spotty majority of which I was a member, I suspect sex remains an occupation undertaken only by other people.
As men get older and the siren call of cocoa and slippers becomes ever more seductive, still there is a pathetic requirement to sustain an image of potency.
Judging by the experience of my peers, there are those who have traded in a partner for a younger model, with the consequent late surge in activity, boastfully communicated at the bar. And then there are the rest, with their growing interest in the shed.
Of course, that the gap between the sexes' special numbers is officially narrowing has had many a commentator excited. But maybe it is simply a case that both sides are just being a little more honest than in the past.
Whatever the cause, most of the British public studying the new survey must have been gripped by the same thought as me: so that explains those strange gurgling noises coming from next door.
Hannah Betts, single
Here I am, 42, lone living, single until proven otherwise, sound of limb and active of sex life. I am a feminist, of an age group that takes contraception and sexual equality as a given, in a metropolitan cohort in which being single is the norm.
This, for a start, marks a change. As the survey notes, the proportion of participants aged 16 to 44 living with a partner has fallen to 52 per cent of men and 54.5 per cent of women over the past two decades, from 57.7 per cent and 64.7 per cent respectively. Some of these solo dwellers will be "seeing" people, others not; either way, for whatever reasons, we are a generation of lone rangers.
Unless, one has chosen to be celibate (quite the risque perversion among post-Boomer generations), this prolonged singledom means one accrues more partners. Traditionally, women have under-reported their "number", men exaggerated it. Among sexperts, the adage was: "Double the female figure, halve the male."
A quick calculation based on single women of my acquaintance in their 30s and 40s comes up with the following: by the mid-30s, the number of sexual partners is likely to be 15-ish; by the mid-40s, it looks more akin to 25, on the basis of the typical sort of life in which one has been monogamous and single. That said, when listening to people talking about their own "statistics", I was also offered the answers "fewer than five" and "70 to 80".
As a married friend says: "The truth is, it varies, just like how often you go to the gym. Sometimes you get into it and go a few times a week, but then life intervenes and you stop." Similarly, for the single, there may not be anyone of interest about for a while, and, then, wham (bam, thank you Ma'am, etc).
One area in which I am letting the side down is sapphic activity. One of the more obvious findings was an increase from 4 per cent to 16 per cent in the proportion of women having had sex with another woman. Personally, I may not be cutting the mustard, but there is evidence of "late-onset lesbianism" - short-lived and sustained - in my circle and very happy they are, too.
It's an old chestnut that women's sexualities are "more fluid", and one that can too easily fall into patriarchal assumptions about females being all body. However, the women I know do appear less stymied by defining themselves via the people that they are sleeping with, less concerned with transforming sex acts into identities, more open to individuals rather than affiliations.
Radhika Sanghani, young
I was in Year Eight when my best friend lost her virginity. Then 13, she told me about it over MSN instant messenger an hour after it happened. She had decided to have sex with her boyfriend after eight months together. They broke up in Year Nine.
In my all-girls private school, having sex was shocking news. Most of us were virgins - we had barely had our first boyfriends. But in the next few years, everything changed; as everyone started their GCSEs, they started having sex, too.
So I'm not surprised to learn that the average age for youngsters to lose their virginity is now 16, compared with 19 for those who are in their 60s today.
But that didn't mean my cohort wasn't responsible. Most were on the Pill and all used condoms. None of them slept with their boyfriends before their six-month anniversary (or so they claimed).
Grades still came first and, during GCSEs and A-levels, sex was slotted in between revision periods.
Our favourite lunchtime topics were, "So what base have you been up to?" and "Oh my God, do you think you're ready to do it with him?"
But for every four of my sexually active friends, there was always one who didn't have a boyfriend or was only slowly making her way up the "base" ladder. I was one of those girls. I didn't lose my virginity until I was 19, to my first serious boyfriend. Among my schoolfriends, I was thought of as a late bloomer.
It was when I got to university that everything changed. In this semi-adult world, there was an ingrained pressure to have casual sex and one-night stands.
Even in the five years since I left school, the pressure has intensified to the extent that sex is no longer an option for teenagers - it's a given. As one 16-year-old girl told me while I was researching my book: "You have to have sex with your boyfriend or he'll tell everyone on Facebook you're frigid!"
In my last year of university, some of my male friends finally abandoned the "lad" stereotype and also began experimenting sexually.
Not having sex, or even not being open to sexual experimentation, is the new taboo among young adults.
Bonnie Greer, silver
At a conference on "intergenerational economics" that I was a part of recently, a woman raised her hand and said that she had been born in the luckiest year: 1948. So was I. We have had the full benefits of the welfare state from cradle to grave. We were the post-war fresh start our parents wanted and needed.
We had options, too. We could either imitate our parents or not be our parents at all. Science was moving at such a pace that the world stretched out before us, ready to be shaped by us. Life has been as we wanted it to be.
Some of us, the "Silver Splitters", have even decided to bring down the curtain on our marriages instead of celebrating that ruby wedding anniversary.
It's scandalous, but when have we baby boomers not been?
Now, I understand that your average 60-plus woman is not a Metropolitan Late Lifer who sheds her husband as easily as her slippers. But here's some breaking news: we are the generation who shortened our skirts; grew (or cut off completely) our hair and above all, had - indeed often had - sex.
Why would we stop? Because we're old? Careful, now, you're talking about my g-g-g-generation.
Essentially we baby boomers emancipated our sex - and women could now have sex purely because they wanted to. Before my generation, women died from botched abortions, in childbirth, no better than cattle whose "bride price" often was our virginity - and by definition our youth.
I'm not saying that this has come to an end, because it hasn't for the majority of women in this world. But a marker has been laid down. We will not go backwards.
You revel in what matters: directness; honesty; knowledge; and daring. There's nothing more exhilarating to me than to see a person - like my husband - ageing naturally and gracefully. The face itself takes on the ancestors, and the familiarity is a good thing, too. A strong thing.
Of course, being the daughters of women who were solidly rooted in the "keep it down and keep it quiet" Fifties, most of us baulk at being "unseemly" regarding this subject. But don't for a minute think we older women live in some sort of sex-free zone. That belief is both dumb and dangerous.
A landmark survey has shed light on Britain's sexual habits. The National Survey of Sexual Attitudes and Lifestyles, which questioned 15,000 people aged between 16-74, found that the average number of lovers for women has doubled since 1991 from 3.7 to 7.7. The rate for men increased from 8.6 to 11.7.
With greater independence, women are experimenting more with different partners before they cohabit or have a child. And that includes experiences with other women, with 16 per cent admitting to same-sex encounters, a sharp rise from 4 per cent in 1991. The number of women enjoying these same-sex relations (which includes kissing) now exceeds that of men, which rose from 6 per cent to 7 per cent.
Overall, however, the number of times people have sex has dropped to less
than once a week, compared with five times a month in 1991. Among older people, 60 per cent of men and 40 per cent of women aged 65 to 75 are still sexually active.
Disapproval of infidelity has grown, with 62.5 per cent of men and 69.8 per cent of women saying it is always wrong, compared with 44.7 per cent and 53.2 per cent in 1991.