Oh what guilty pleasures were to be had on TV last night, and I'm not even talking of the adult sibling incest documentary, entitled, with Channel 4's usual coyness, Sleeping with My Sister, although I'm ashamed to say I did enjoy some of its tragicomic moments. More of that later.

No, I'm referring to the - you really really shouldn't, you bad bad thing, they're only teenagers for God's sake - forbidden fruit of Gossip Girl (ITV2). This is the series that has unexpected groups of Americans abuzz - from serious critiques in the New Yorker to gay men's blogs on subjects such as “OMG - The Boys of Gossip Girl All Have Chest Hair!” It's odd, given that this appears at first to be a silly high school show along the usual formula. But not, if you understand it as glossy, intergenerational porn.

Never has a series so pushed the limits of fantasy in re-imagining the lives of teens: airbrushed out is all the badly co-ordinated, bad complexioned loafing around shopping centres that characterises the period for most. These characters, ranged around the heroine, the glamorous blonde Serena van der Woodsen and her arch nemesis, the brunette Blair Waldorf, are rich and luscious beyond compare. Even their names are so expensively camp as to make a drag queen jealous. They frolic in a Manhattan playground of unlimited drugs and designer clothes, making Beverly Hills 90210 look like Grange Hill. Imagine a show about the schooldays of Paris Hilton or Ivanka Trump, except, you know, classier, better looking and better dressed.

Why is it a big hit with twenty and thirtysomething adults for whom the subject matter is age-inappropriate? Drooling over teens? At least everyone in Sleeping with My Sister is a consenting adult! But what escapism is there for the old on television? Take something apparently glitzy such as Sex and the City. For the middle aged to watch other women, pushing 40 and plagued by feelings of doom and self-doubt, was a little too real to be enjoyed with a vodka martini, no matter the number of covetable shoes.

How much more enjoyable to watch the same kind of scene, but as played out by the underage? Relive your teen years, but now with Botox! Gossip Girl borrows a lot of devices from shows such as Sex and the City and Desperate Housewives, but without having to see the actresses' raddled faces remind us of our own. In Gossip Girl, Blair's mother tells her, “you'll never be more beautiful, or thin, than you are right now”, before scolding her to “put more product in your hair”.

To add to the unseemliness of it all, the plot actually encourages us to think of the children as adults. Making them super-wealthy is a neat device; their money allows the characters to play at being grown-ups more effectively than most grown-ups: the hormonally teenage conversations are held while sipping cocktails in exclusive bars. The teenagers in the show are playing at being adults, while the actors who play the teenagers are in their twenties.

Confusing? Intentionally so. Addictive? Yes. After five minutes of watching, I wondered if I could make it through an hour of such tosh. After 25 minutes, I wondered if I could make it through the week until next time. Then I took a shower, repented, and said a Hail Mary.

Cutting Edge: Sleeping with My Sister was supposed to be a serious examination of the phenomenon of “Genetic Sexual Attraction” (GSA) whereby siblings who have never known each other as children, meet as adults and fall disastrously in love. But even the most savagely satirical playwright would not have put these words in the mouths of Nick and Danielle, the Scottish half-brother and sister, in response to police prosecution: “What right have they to split the family up... it's wrong to keep family apart.”

Or again, in the case of the US case study, Tom, who was reunited with his siblings in their thirties. He claimed that GSA was at work, but how does that explain him choosing one of his half-sisters over the other - a new spin on the age-old family jibe of favouritism? I would have liked to have heard from the other sister, or indeed any of the other relatives (especially Nick and Danielle's mother, who found her children having sex on the sofa days after they were introduced. How does that feel?). I'm all for understanding difficult topics, but without this, it felt too sympathetic.

Out of the Box

So, farewell Ashes to Ashes, which, despite “differences of opinion” among viewers, was the most successful drama series launch of this year. That means a second series starts filming in August, and that means that for fans of “closure”, the last episode would have been unbearably frustrating. Don't forget that “closure” wasn't invented in 1981.

Why is it that The Apprentice hasn't worn thin, like so many other reality shows? The first episode of series four on Wednesday got a record 6.4 million viewers, compared with 4.5 million on the last series. Tight editing and great cast selection have something to do with it, but the producers urgently need to think up new tasks. I think all of us have tired of watching contestants become home shopping presenters, or the sight of men in hairnets running a market stall.

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