Get ready to singalong-a teenage sex education

Going all the way: Glee's gay couple Kurt and Blaine (Rex Features)

Things are getting serious for the all-singing, all-dancing school kids in Glee. A controversial episode featuring a straight and a gay couple each losing their virginity has been praised for its mature attitude towards adolescent sexuality.

The award-winning musical-drama series enters unchartered territory with "The First Time", an episode broadcast on Sky1 tonight after airing in the US this week.

The storyline follows long-standing couple Rachel (Lea Michele) and Finn (Cory Monteith) deciding to go "all the way" after being told their performance in the team's production of West Side Story lacked authentic sexual fizz. But the boundary-pushing show has married this development with teenage gay couple Kurt (Chris Colfer) and Blaine (Darren Criss) also deciding to have sex.

The virginity "double header" may prompt some candid discussions among parents watching with younger children. Yet from its launch, Glee has embraced homosexuality, explored the consequences of teen pregnancy and placed characters who might be outsiders in other series, firmly centre-stage.

Ryan Murphy, Glee co-creator, said: "Everybody has seen a straight couple losing their virginity, but has anyone dovetailed the gay and straight stories and given them equal weight? That seemed like an exciting choice."

Murphy's "exciting choice" was however condemned by the US-based Parents Television Council as "reprehensible". Speaking before the episode was broadcast, the group's president, Tim Winter, said: "The gender of the high school characters involved is irrelevant. Research proves that television can, and likely will, influence a teen's decision to become sexually active. Fox knows the show inherently attracts kids."

Another US watchdog, the Culture and Media Institute, accused the Fox network, part of Rupert Murdoch's News Corporation, of waging "a relentless campaign of liberal propaganda and pushing the boundaries of what's acceptable on broadcast TV."

The reality was somewhat different. The gay sex scene arrives after the couple visit a gay bar in a bid to inject some spontaneity into their love life. They reject the temptations on offer and decide what they have together is sufficient. The actual sex depicted offers little more explicit than a nuzzling of noses.

To the musical accompaniment of "One Hand, One Heart" from West Side Story, their compatriots Rachel and Finn take the plunge after committing themselves to safe sex.

For both couples, the episode shows the importance of discussion and emotional preparation before taking such a big step. Yet awarding the gay scene equal status to the straight couple's encounter is something US viewers have not seen during a prime-time drama.

Reviewers praised the episode for handling the sex scenes delicately. The influential E! entertainment site concluded: "Though sex is certainly the word of the day, the episode gives both couples more depth of emotion than we've seen so far this season."

Since its launch in 2009, Glee's colourful dance routines and singalong cover versions have helped shift 30 millions albums. But the series has been shedding US viewers during its third season as Murphy steers the drama into more adult territory. Former cheerleader Quinn Fabray, who gave away her baby, is now engaged in a custody battle to win her back.

The virginity episode may be too tame for viewers who enjoy Glee's more subversive moments. Website Jezebel argued: "If anything, the sex is too romantic and unrealistic, but that's probably smart when you're trying to show America that there's nothing scary or uncomfortable about gay teens in love."

"The First Time" was seen by some as an attempt by Murphy, who has created a new hit show called American Horror Story, to reignite viewer interest. Even the actors were expecting some nudity. Colfer said: "What I thought could be raunchy and over-the-top was just very sweet and emotional. That's kind of how it is with Glee. I think it's a huge deal that this is the first time something like this has been shown, but it's handled so delicately that I don't think it will have quite the shock factor that people are thinking."

The "virginity losing" scene is a mandatory development in US teen dramas but producers often struggle to find new plotlines once the "will they/won't they" debate is resolved. The popular Dawson's Creek delayed the big moment between Katie Holmes' Joey and Joshua Jackson's Pacey until series four.

The Daily Mail website, normally a reliable arbiter of moral outrage, warned viewers that Glee would unveil an episode "involving gay sex, premarital sex and underage drinking". But it is a measure of Murphy's success that the writer was forced to conclude: "There is apparently no sensationalism here."