Larkin was wrong. Sex in Britain did not start in the 1960s. It began in the 1970s and we can even name the place – Wimbledon; the shared fantasy – Chris Evert; and the most famous promotional poster in the world – the Tennis Girl.

You don’t really need me to talk you through the Tennis Girl, do you? Surely everyone remembers the girl at the net, one hand lifting her dress to reveal a gloriously bare bottom while the evening sun streamed across the court. Oh, all right then, if you must. It’s www.the-tennis-girl.co.uk.

The picture had, said its photographer, schoolboy appeal. Martin Elliott shot it, using his girlfriend as a model, on Birmingham University’s tennis courts in the summer of 1976. Thirty years after its issue by Athena, the poster remains one of the world’s biggest sellers, an iconic image that has been parodied by dozens of cartoonists; and reproduced a few zillion times by other photographers hoping some of the magic would wear off on them. Even Kylie Minogue adopted the pose for a GQ cover.

Which rather proves its appeal extends beyond schoolboys to big boys, and even pensioners.

Now I’m not delving into all this in order to titillate. Far from it. Rather, on the day on which Wimbledon starts, I want a serious answer to a serious question: why tennis? What is it about the game, and the dear old British psyche, that makes it the ultimate aphrodisiac? (We will leave Betty Stove out of this column). Now everyone, both men and women, understands that men’s tennis has to have a certain amount of airtime.

Therefore, we’re politely interested in the story of Murray’s wrist. We will anticipate, mildly, the arrival of Roger Federer on court today in his mystery designer gear. But male tennis players, these days, are a rather dull sideshow in the fairground of life.

The female players, on the other hand, grow more must-see every year, and an increasing number of authoritive voices in the game now acknowledge that they carry the promotional load, bringing fans through the turnstiles and gaining television ratings. Why? Because sex sells.

By a happy collision of sport and culture, the women have struck gold in this celebrity-ridden, appearance-obsessed age. They are Hello! magazine made flesh; the Oscar ceremony with short frocks; soft porn without the embarrassment. We want to admire their figures, check out their outfits, see how good their legs are and listen to them grunt. Wimbledon, if we are honest, is to sex what Glynbourne is to opera: it’s the nearest that women get to staring at other women’s bodies without feeling self-conscious; and it is the closest that your average respectable men gets to lap dancing.

After all, where else in this world are men going to have, at such close range, supremely fit, attractive, energetic young women with bare limbs and big cleavages running around panting – just for their entertainment? And in a situation where – bliss – they don’t have to tell lies to their wives.

So this is my theory, first formulated in a dismal disco at Aughton Lawn Tennis Club circa 1973 and honed every year since. The Wimbledon championships have been a metaphor for English sexual emancipation for as long as they have existed. By the behaviour and dress of the players, one can gauge the growth of sexual maturity, if not psychosexual health, of a nation.

In the beginning was only repression. Women competed in the equivalent of burkas, emancipated only when Suzanne Lenglen arrived revealing bare arms and calves. Men protested the most, just as they enjoyed it more.

After the war, female tennis passed into a safe, matronly era, with women who must, I suppose, have been young but looked forever middle-aged: Anne Jones, Billie Jean King. Virginia Wade represented the last of that era.

And then came the revolution. Chrissie Evert was a young, kohl-eyed American for whom everyone, of both sexes, developed an instant crush. For teenagers, she was our punctuation, our landmark on the road to adulthood. We devoured her Florida-brown legs, her femininity, her bobble socks, her hamster face, her blonde hair, the beguiling sighs she made when she hit the ball.

Looking back, I think the British reacted to Chrissie the way small town America responded to the sight of naked African women’s breasts in the National Geographic. She was our learning curve; our coming of age; our forbidden window on the world.

And if Miss C. M. Evert was the first tennis totty, who paved the way for the girl power that followed, I’ll bet she was also the inspiration for the Tennis Girl. Martin Elliott concedes the universality of his poster, saying that it’s “one of the world’s fantasies that you are going to see up a woman’s skirt”.

Ask any photographer who’s covered Wimbledon why he enjoys it so much, and he’ll admit precisely that (and tell you that, by the way, Steffi Graff had the best legs ever.)

Tennis is about rules, control and repressed passion. It is, covertly, absolutely all about seeing up girls skirts. What Chrissie began, reached its most overt in the Williams sisters, whose physicality, skin colour and spray-on dresses brought male Middle England to the brink of heart failure. The best thing were the hilariously euphemistic complaints about the sisters’ grunts, which plainly reminded the chaps of all the porn films they weren’t allowed to watch.

This year the All England Club have given the women parity in pay for the first time. My case is made. Enter the showgirls. Wimbledon fortnight, so eagerly awaited, so rich in airtime, so sought-after for tickets, so redolent of propriety, is underneath it all a seething mess of raunchy schoolboy fantasies. The festival of the Tennis Girl, no less.

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