“You like talking about sex, don’t you?”

“I do,” Jonni says, with a triumphant grin.

We’re eating supper at my home. He sits at the head of the table, me to his side. “It’s something that I know really well. I’ve been having regular sex since I was 12 years old. I just always seem to attract it.” Jonni, 18, a singer from Hertford, is painfully Hoxton-trendy, his hair laboriously thickened and asymmetrical as he talks, in his gravelly, mockney boarding-school drawl.

Threesomes, sixsomes, bondage, married mums: it would be easier to tell you about what Jonni hasn’t done. Does he think his generation is different? “Yes. It’s just the amount of sex they’re having from a young age. There’s no shock factor in sex any more. People are very promiscuous at my age. There’s a lot of casual sex now. It’s all become much simpler.”

Generation YouTube is frighteningly frank, terrifyingly knowledgeable and shockingly experimental in its range of experiences. “In the kitchen, at the beginning, when you were talking about how you’d lost your keys and stuff, I was just standing there thinking, ‘This girl is hot. Like incredibly hot. And she understands me.’

“I like people to be impressed by what I do. It’s an exhibitionistic thing,” he tells me, as he flirts over sticky toffee pudding (forgoing the cream so as not to put on weight). “So you like to be adored and recognised and sex gives you that?” “Sex gives me that. Music gives me that.”

The Stanford University sociology professor Paula England, who has looked into the phenomenon of the “hook-up” – currently trouncing the “date” among young people – sees seismic shifts between Generation YouTube and its predecessors as a result of its willingness “to engage in casual sexual behaviour with strangers in semi-public places, at parties for instance”.

Jonni tells me about the time he had sex with an American girl while five of his friends were in the room. “Public sex happens all the time. On holiday. In house parties. At sleepovers. You can’t avoid it.”

Jonni doesn’t want his mother to read this article. “I’m actually quite scared about reading it too,” says his mother, a vivacious, committed and immaculately presented yummy mummy in her early forties from Knebworth in Hertfordshire. She was aware that Jonni was sexually active from a young age. “I think he began having sex when he was 13 or 14. Not full sex, but he was dabbling.” She tried to talk him out of it, which had the effect of making him more secretive. “I kept saying, ‘You are far too young to be doing this; just wait a while, you’ve got your whole life ahead of you.’ He kept much more quiet after that.

“I’d rather not know too much. I don’t think it’s good to be their friend.” Matters became hard to ignore, however, when Jonni was 14 and a girl in his class bombarded their house with phone calls every night. “She was pestering him and he was trying to get me to lie. I said, ‘If you don’t want her to ring, you need to speak to her.’” Jonni’s mother listened in on the call and was shocked to overhear the girl telling Jonni she would give him oral sex if he would be her boyfriend.

“It was so matter of fact. I came downstairs and my partner asked if I’d seen a ghost. To which I replied, ‘I just really wish I hadn’t heard that.’ Girls dish out blow jobs like kisses now.” Jonni was mortified when his mother reported the girl’s behaviour to his school. “I’ve come into the 21st century with my eyes wide open as far as sex is concerned,” she says. His mother was careful not to endorse Jonni’s sexual antics until he turned 16. From then on she was very keen to instil the importance of safe sex – ensuring there is always a ready supply of condoms in the house. Perhaps as a result, Jonni always uses contraception – and at 17 he even had himself circumcised for hygiene reasons.

Jonni’s mother sees big differences between Jonni and his brother of 15, who was raised with the internet and magazines such as Nuts and Zoo. Jonni is far more romantic. “He used to go to summer camps when he was little, and on every holiday he fell in love and would come home in tears. I used to look at him when he was little and think, ‘He’s gonna be a womaniser, that one.’ Some boys, all they’re interested in is football. Jonni wanted to kick the ball and hold the girl’s hand at the same time. I worry so much about the boys, I’d hate to be bringing up daughters in this age.”

In the UK in the 1950s, people tended to have sex for the first time in their twenties: men at the average age of 20, women at 21. Now it’s around 16 for both sexes. Generation Y – those born after 1980 – are revisiting the sexual free-for-alls of the 1960s, unlike their more uptight, relationship-oriented (or, as some might see them, dull) predecessors, Generation X, for whom the threat of Aids loomed over their first sexual experiences and ideas. But if promiscuity is rising, so too is awareness – British teen pregnancy rates (previously the shame of Europe) have fallen by as much as 40% to record lows. Teenagers may now be doing it younger, more frequently and more deviantly, but three-quarters are using protection during first sex. “You realise there was no internet 30 years ago?” the 17-year-old A-level student Sophie says, as if stating the unfathomable.

There is an air of excitement tinged with panic when I visit her Surrey home. It is the calm before Sophie’s 17th birthday party (themed “rock stars and porn stars”, though her parents, an architect and housewife, don’t know).

“It’s not like in the olden days when it was like, ‘Oh, please tell me what it’s like to have sex!’ If I wanted to know I could just go online and talk to somebody random. There’s so much information, even in school. When you’re 10 they tell you how to have sex, what drugs give you which effects and what alcohol does to you.” Sophie is petite and sultry, with bright eyes that dance as we speak. She is part of the “first true internet generation”, says the London School of Economics cyber-psychologist Professor Sonia Livingstone, who specialises in teenage internet use. “It’s the ones who are 16 or 17 now who can remember it first coming out in their schools.”

As I sit with an excited Sophie on her bed, with its pink duvet and the odd cuddly toy, “Chloe Corpse” – Sophie’s 14-year-old sister – and her boyfriend, “Drop Dead Adam”, Identikits of each other with their kohl-black eyes, pale faces and backcombed hair, barge in and out to check their reflections in the mirror. Chloe rolls her eyes with delight behind Adam’s back and mouths “He’s gorgeous” at me.

Parties of the scale to which Sophie and Chloe are accustomed were not common five years ago. Those were in the years BM – Before MySpace. “I started getting more boyfriends after MySpace came out. It just happened out of nowhere. We were going to gigs and parties every single weekend. I rarely have a Saturday night in, and if I am in, I’m having a house party!” Sophie shouts, throwing her hands in the air. Perhaps her parents seem apprehensive for good reason. They have only just recovered from Chloe’s 13th birthday party almost two years ago. “MySpace had just come out. People started breaking in through the door. Kids were getting sick – one girl got paralytic and had to be taken away in an ambulance.”

At Sophie’s last party, “Everyone ended up stripping and getting off with each other – whether they were gay or straight, they were changing their personalities.” Sophie estimates that she “got off with at least a hundred” boys last year. “I just like meeting guys and making out with guys. It doesn’t matter if I’m in a party, if I’m on the Underground, it’s wherever I feel like it.”

Sophie counts Lindsay Lohan, Paris Hilton and Jeffree Star (“a man who looks like a woman with pink hair who’s got, like, nine million friends on MySpace”) among her favourite celebrities. It seems kids love adults who behave like teenagers. (Which famous face did the boys I spoke with unanimously like best? Russell Brand, of course.)

Inevitably, the media and entertainment industries have a huge bearing on teenage social norms. While yesteryear’s Grange Hill’s most shocking storyline was Zammo selling drugs, today’s Skins shows teenagers changing beds more often than their knickers. Dr Arthur Cassidy, a psychologist at the Belfast Institute who specialises in teenagers and sexuality, explains that celebrity is a key issue. “There is a media fascination with who celebrities sleep with, and teenagers see that as a bible for how to live.” The message of love and romance in 1970s teen magazines changed to themes of lust, prowess, experimentation and masturbation over the ensuing 20 years.

“When I was little,” Sophie recalls, “seeing the Spice Girls changed the way I dressed. I started wearing tighter clothes. Tonight I’m wearing a corset, suspenders and fishnets. It’s the least amount of clothes I’ve ever worn in public, but I don’t care, because I think that in this day, girls should be able to wear what they want, and if I want to dress like a porn star for the night, then I’m going to do it!” Chloe, meanwhile, is wearing a see-through black-and-red negligee that just skirts her bottom.

As the teenagers arrive for the party, they divide themselves into groups of boys and girls. Some compliment each others’ hairstyles, discussing backcombing techniques and how to stop their make-up running. That’s just the boys, who look like they’ve styled themselves on A Clockwork Orange and The Seventh Seal. The girls are tucking into WKD and vodka cocktails, looking painfully thin and in need of clothing.

I talk with a sensible girl dressed as neither a rock star nor a porn star about A-levels and job prospects, asking whether she has a sibling: anything to divert from the fact that she is being studiously ignored by the groups of girls gyrating near-naked in front of the boys, wearing beyond-their-years expressions. Two boys writhe and caress against the wall of the kitchen: one has his trousers undone. Sophie is flirting.

Girls march their boyfriends into public view before tonguing them languidly, yearning to be watched and wearing self-congratulatory expressions. I am feeling somewhat out of place against a sea of corsets and bottoms and breasts. As I’m leaving, a boy grabs me and asks whether we can talk about him being gay. I oblige and he leads me upstairs, past the hordes filing into the bedrooms, and into Chloe’s room. I accept Drop Dead Adam’s offer of a vodka and a boy whoops: “She’s wicked!” A gamine sylph with ivory skin and dyed raven hair skips in and coos: “Interview me, I’m half gay.” A small 14-year-old punky girl follows – there are murmurs of approval from the boys about the time the two had oral sex, as the pair lock lips for a slow kiss. I explain that I should be getting my taxi and everyone follows, except for the tall bisexual girl being helped onto Chloe’s bunk bed by a pretty blond boy before descending into an embrace.

As I’m waiting by the door, a grammar-school girl with an ethereal 1960s beauty tells me she’s cold and bored. “Why don’t you talk to some boys?” I suggest, observing a girl heavy-petting with a gay guy and her boyfriend. “There’s a lot of competition here,” she says, glancing towards the ash blonde in French knickers and fur coat being led up the stairs. “But you’re beautiful,” I tell her. “Look at them,” she says. “They all want to be noticed, they all want to be different. Being sexual in public is another way of getting that attention.” And then, setting eyes upon two girls kissing, “The most effective way to do that is with someone of the same sex.”

“Nobody cares about sexuality. I think it’s hot if two buff guys make out,” says Sophie. “I get with girls. I got off with a girl from Sweden who had pink hair and my friend taped it and put it on YouTube. There’s no secrets on MySpace.”

Dr Cassidy told me there is mounting evidence of teenagers experimenting with people of the same gender. “It’s a relatively new phenomenon that might well continue,” he says, citing the adaptations to multiculturalism, gender and technology that Generation Y, who are “growing increasingly skilled at coping with dual identity,” have made. “There is a value system surrounding trying things on: if it’s fashionable, we’ll try it; if that doesn’t work, we’ll try something else.”

A survey from Oregon University confirmed that same-sex behaviour is increasing, indicating that bisexuality is more accepted among the young than it used to be. That sexuality is now cited on every social-networking profile (in contrast with that civic favourite: race) could also be an influencer; not least in the easy approach to sexuality that the teenagers display.

“Some girls will say, ‘Look at me: a girl getting off with a girl is a turn-on.’ But I quite like girls. I was kissing a friend at a party and I knew it wasn’t a show of attention.” Kate, a 19-year-old student, and I are sitting on the bed of my B&B in Exmouth. She is a practising Christian from Newport, Wales, and says that sexuality in religion is a matter of “changing and evolving with the times. A lot of Christians are growing up and accepting that there are no boundaries in love. Girls get off with other girls: it’s no big deal. I’ve slept with a girl, kissed her and stuff – it was fine.

People can be friends and sleep with each other and it won’t matter. They’ll wake up the next day and go, ‘I can’t believe I did that,’ and it’ll just be funny. I get to that stage where I’m really drunk and I want to have sex and we’ll do loads of stuff, but I won’t actually have sex. We were brought up with this undertone of not having sex with too many boys, but no one ever said don’t have oral sex or don’t take all your clothes off and do everything else. It’s new times; new horizons.”

The Sun’s agony aunt, Deidre Sanders (Dear Deidre) – to whom the teenage voices among the thousand-strong letters she receives every week increasingly speak of erectile dysfunction, body anxiety and threesomes – says that in many ways she is “glad to see much of the guilt there used to be surrounding sex eradicated; there’s a greater tolerance toward homosexuality and bisexuality”. Sex for teens today “is a sport at a time when hormones are high and emotions fragile”, and is increasingly detached from relationships. Paula England’s studies found that mating has replaced dating as the preferred way for kick-starting relationships among the young.

A spokesman from the Department for Children, Schools and Families – which has been re-evaluating its sex-education strategy for the past decade against a competing landscape of Facebook and Britney Spears – told The Sunday Times: “Good sex education gives young people the knowledge, skills and confidence to delay sex until they are ready to make informed decisions. It also helps them resist pressure and take responsibility for their sexual health when they do become sexually active.”

In contrast, Tony Kerridge, from Marie Stopes International, thinks British children “are being failed on a grand scale” by the current sex-education system. He cites the “classic” example set by Holland, where sex is spoken about openly in the home and education is introduced far earlier. It has the lowest rates of teen pregnancy in Europe and a higher average age of first sex.

Many blame the traditional British awkwardness surrounding sex as the catalyst for our seeming inability to control the sexual appetites of our teens: “Sex education begins in the home, but the British, particularly the middle classes, have this embarrassment regarding sex,” says Kerridge. “There’s this postcard humour, a sense of hiding behind sniggers and euphemisms. I think it’s time we took a more adult approach to sex and really begin to see the impact on our children’s lives.”

The trusted panel’s view? “Public-school kids are mostly into drugs, mainly because they can afford it. The grammar-school kids are more boring, and the comprehensive schools are mostly into sex,” says Sophie.

The concept of the male holding out for sex is a relatively new phenomenon, but one that is strangely apparent among the group I interviewed. Look at the teenage members of the growing “straight edge” movement, the manifesto for which stipulates no alcohol, smoking, drugs, or sex outside of a committed relationship. “There’s a lot of stress involved with corruption. ‘Shall

I tell my mum or go home and cover up? Will I get found out? Where will we do it?’ Being straight edge, all those worries are just gone.” The A-level student Joe, 17, lives in Leytonstone and is both a virgin and pin-up handsome. His friends call him a pussy for not having sex. He’s had girlfriends who wanted to “but I was just like, ‘Nah, I don’t think so.’ I think of sex as the most intimate thing you can do with someone, and that should be valued.” He is curious: “I have thought, ‘I suppose it would be quite good,’ ” but he worries he’ll regret it, like many of his friends. Perhaps it’s overrated, he thinks. He has gone to second base – “Second is about exploring each other’s bodies” – but stops short of oral sex. He likes doing second. He would like to try it more.

I’m starting to think that Joe isn’t real until he says he watches porn. “A lot. It’s educational,” he grins, his eyes lighting up. Surely porn isn’t straight edge? “Come on,” he rolls his eyes. “Everyone watches porn. I’d rather watch porn than do it to someone. It’s weird that you can only watch porn when you’re 18, but have sex when you’re 16. It should be the other way round, shouldn’t it?”

“Children can be looking at amazingly hardcore stuff every night and their parents will have no idea,” says Deidre Sanders. Joe’s mother does not think her son watches porn, while admitting that as a single working mother of three, it’s occasionally easier to put the kids in front of the TV or computer while she’s cooking dinner. She tries to promote open conversation about sex, while emphasising its importance within a loving relationship. “Nowadays teenagers form their ideas of what sex is from the internet: they think it’s normal to be having threesomes,” says Sanders. “There is this sense of some parents having lost the authority, that they simply don’t know how to cope with the issue, of throwing their hands in the air.” The issue is particularly pronounced among single working mothers (girls from single-parent families are far more likely to have sex younger than those raised by a father and mother in the home). “There’s the sense of ‘Do as I do, not as I say.’ If a teenager has known their mother to have had five different sexual partners, they will argue that they are entitled to do the same.”

So the fact that Generation Y’s first glimpses of sex are now drawn from pornography will undoubtedly have an effect on those who are part of it. A fifth of 9- to 11-year-olds questioned in Sonia Livingstone’s seminal UK Children Go Online 2004 study had seen porn online, rising to 60% of those aged 12 to 15. Rare is the 19-year-old who hasn’t watched porn. Close to half believe they were too young to have viewed it when they did. The ever-popular YouPorn, and its counterpart XTube – where amateurs, including young people, show and do all for the camera – have proved hits among teens. Clinical psychiatrists are dealing with spiralling numbers of boys addicted to pornography. Jonni began watching porn at 10 and believes it shifted his perceptions enormously, making him “very, very comfortable with sex from a young age”.

The passport to sex that the internet provides is something Livingstone sees as a double-edged sword. She stresses that sexual people will seek out sexual information, but wonders “whether the internet introduces information and expectation too early, leading teenagers to think sexual experiences are more normal for their age group than they are, in turn pressurising them to become sexually active. On the other hand, they’re shown to be given support and advice”. Take, for example, the teen forum I read where a child detailed her concerns about whether to start shaving her pubic area. Her conflict lay between fears of her mother noticing and pressure from her peers, even though she wasn’t sure whether she’d begun developing or not.

Raised on a diet of porn and mixed messages, teens are determining their own rules, with more changes afoot. For if today’s A-level students are the first true children of the cyber age, “We’re seeing a new generation of 10-year-olds who can’t imagine living without it,” says Livingstone.

Sophie’s party was, by all accounts, “well jokes”. Her parents came home at 2am to find four teenagers about to embark on a mini-orgy in their bed. “It’s ridiculously sexual, but it’s celebrating the fact that no one cares any more,” she yells, bouncing up and down on her pillow. “No one cares whether you’re a boy or a girl or if you’re gay or straight. It’s just, like, do what you want with whoever you want. Wear your hair pink, have the crazy make-up, listen to trashy music. Who cares any more?”

The portraits on these pages are of the young people interviewed by The Sunday Times Magazine, but the pictures have been doctored to protect their privacy

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