Nick is sitting on a sofa, topless, fiddling his way through an iPod. Joseph and Mike are tucking into a Domino’s pizza.

Larissa is tying up an impressive, limited-edition Nike high-top, and Hannah is fiddling with her hair. As 18-year-olds go, the Skins cast are pretty much behaving to type.

On screen, the story is more dramatic: they pop pills, trash their parents’ houses, drive cars into lakes, struggle with anorexia and develop uncontrollable crushes on one another. Yup, they’re badly behaved teens, but they are also bright, beautiful and cool – and the show is surprising not for what they get up to, but for the insouciant, knowing and frighteningly assured way they behave. They are questioning, perceptive and nonconformist. If you’ve encountered any teenagers recently, you’ll recognise the type.

With the first series of Skins last year, Channel 4 took a bold step on behalf of teenage Britain. It set about creating a show that would not just reflect a generation, but also refuse to patronise it – characters who not only looked like Bristol teenagers, but spoke, dressed, had casual sex and socialised like them. Postwatershed, they were allowed liberal measures of partying, a groovy soundtrack and a vernacular that was shaped with their peer group in mind. What This Life did a decade ago for 1990s metropolitan twentysomethings, Skins is now doing for Noughties teens. It has become its own moment.

Of the actual teens, Nicholas Hoult was the only “name” attached to the project, having previously starred as Hugh Grant’s odd-looking child friend in the adaptation of Nick Hornby’s About a Boy. Hoult swaggers his way through Skins series one as Tony, the amoral, cocksure lothario. He plays the sort of urban male who has matured under the pop-cultural preeminence of Robbie Williams and David Beckham: the type who appears to be able to make sexual advances to a table leg, if the fancy takes him. Hoult might be Skins’ most recognisable face, but this was a group effort. And as the season aired, the group started to recognise that the show didn’t just appeal to, but actually meant something to their peers. “You’d find yourself at a party with your friends, and someone would say, ‘Oh, this is a bit Skins,’ ’’ Hoult says.

“There was a time before Skins when teenagers only had American drama to watch,” says Hannah Murray. “But in programmes like The OC, you see the edgy characters talking about smoking, rather than doing it. It can’t deliver, which leaves it in a strange place.”

Murray gave a head-turning performance as Cassie, a messy anorexic who ended up with Sid, a full 10 notches below her in the looks stakes. “I read the script and fell in love with it. I thought, this isn’t about a girl who is anorexic. You don’t have to be anorexic to get it, you only have to understand what it is to be lonely. It was a brilliant piece about loneliness.” And what current teenager, or former teenager, doesn’t know that feeling?

The series invited a similarly casual relationship with narcotics. Joseph Dempsie was cast as Chris, the pill-popping party boy. “Chris is supposed to be a huge druggie, but doing loads of pills just touches on an aspect of him,” he says. “If this had been made 10 years ago, there probably would have been some moral obligation for the TV producers to give him a bad pill and put him in hospital. But it’s different now, and Skins just gets that. People do go out and have good nights on pills without dying. Teen life isn’t quite as bad as tabloid morality has it. That’s why teenagers like Skins. Not that we’re trying to encourage that stuff or anything, but it’s part of reality.”

The cast love this about Skins. Rightly so – it elevates them above the black-and-white moralising of soap, without stinting on the fun. “There aren’t warning adverts after the show, which I think is important,” says Mike Bailey, who plays Sid. “There isn’t some voice coming on after the credits saying, ‘If you’re affected by these issues, then phone this number.’ That’s patronising to the audience. It isn’t issue-led, it’s led by the characters.”

For series two, things have become a whole lot darker. “It is about boys and girls turning into men and women,” says Bailey.

Tony had been knocked down by a bus in the gripping finale of the first series. He isn’t dead, but he is altered – partially handicapped mentally and physically. Again, his redemption is located in a moral grey area. “I don’t even know if I like Tony as a person,” Hoult muses. “He is cocky, difficult, arrogant. I love the way that being hit by a bus doesn’t redeem him; it doesn’t make him a good person. It’s more complicated than that.” Life, you might say, is more complicated than that.

All the cast agree that the show has hit a recognition button for its audience, which, aside from the rollicking drama and rapid editing, is ultimately its triumph. “It doesn’t try to be hip and young,” says Larissa Wilson, who plays the uptight Jal. “It just is. Everyone would trail off if it was trying too hard.”

Hoult pinpoints it more sharply. “As I read the scripts and learnt about the characters, I realised I could point to somebody I knew and say ‘Yep, they’re like that.’ ’’

Skins series two starts on E4 on Monday, February 11, at 10pm. It is repeated on Channel 4 on Thursdays at 10.30pm

Editor's choice

• The End: the worst movie endings ever
• Introducing The Times Proms Podcast
• Heath Ledger tipped for Oscar