As I write this, a pneumatic young couple are writhing in the shagpile behind me. It's all grunts and groans and bodily fluids. By the time I've explained what I'm actually writing about, it will have turned into a full-blown orgy. But you'll be gripped. You'll stay for the explication, because you'll be transfixed by those golden bodies, entangled and unconstrained. That, in a nutshell, is "sexposition": the art of outlining all that tedious plot against a background of no-holds-barred sex. You might have seen a bit of it in Homeland, or maybe True Blood, both currently showing on British TV.

"Sexposition" was coined by the US blogger and critic Myles McNutt to describe the many and varied scenes in the HBO fantasy series Game of Thrones that play out against a backdrop of sex and nudity. "I felt this particular trend within the series was something that we as critics should be talking about," he says via email. "Ultimately the term ended up catching on with some of my fellow critics and becoming an actual topic of conversation."

One of the early adopters was James Poniewozik, the TV critic of Time magazine, who offers his own definition of sexposition: "It's something more than gratuitous or ample sex and nudity in a show – it's using that sex to divert the audience or give the characters something to do in scenes that involve a big download of information or monologue. I wouldn't say Game of Thrones is the first – I think of all the Sopranos scenes in the Bada Bing, with strippers on the pole while two characters discuss plot points, or Deadwood, when Al Swearengen would deliver long monologues to a whore who was fellating him."

Classic sexposition: Peter Dinklage and Esme Bianco in HBO's Game of Thrones. Photograph: Supplied By Lmkmedia

Actually, sexposition goes back further than that, but there's no doubt the US cable channels – such as HBO – that specialise in long-form dramas requiring a serious commitment of both time and mental energy have raised the bar. Long before The Sopranos, cop dramas (especially in the cinema) would routinely feature someone being questioned in strip clubs. British cinema historian Matthew Sweet takes it back further. "I wonder whether the root of it might be from the newspaper comic strip," he says. "Some feeble joke is played out and the protagonist just happens to have no clothes on." That would be George and Lynne, in the Sun, where Lynne – no matter where she happened to be – would somehow find herself disrobed. But Sweet goes back further still. "That itself is rooted in the wartime comic strip Jane, where there would be a moment of nudity not driven by the narrative."

And then he goes back still further. "The nudity in Game of Thrones goes back to something even older – a classical context meant nudity was permissible and casual and everyday, and that comes from 19th-century painting." So what's new about the new wave of nudity? "What may be different here is that you didn't have as much need for exposition in past TV shows," Poniewozik says, "because the narratives weren't as complex. In other words, the sex part is not that new; the position part is newer."

At which point, you might be forgiven for wondering when I'm going to get round to some graphic sexual imagery, instead of having all these critics witter on about historical antecedents. So let's do it. Let's get physical. Let's take arguably the definitive piece of Games of Thrones sexposition, in which the Machiavellian palace fixer Littlefinger engages in a long soliloquy, interrupting himself occasionally to offer direction to the pair of prostitutes whom he is instructing in the art of putting on a lesbian sex show. Classy. But actually, as McNutt explains, it's an example of how sexposition can work to inform us about a character, too. "The Littlefinger sequence is an interesting one in that it has clear thematic implications on his view of power, on the idea of Littlefinger as the prostitute [of the government], always able to convince others that they are in control when it's really a charade."

The problem comes, though, when you can't get through an episode without seeing stiffened nipples during a discussion of statecraft. As Poniewozik says, the individual scenes make sense and are justifiable, but "there are just too many, to the point that it becomes shtick … Relying on it too much kind of insults the audience, suggesting they need to look at tits to keep interest in what is a very sophisticated show." That bit about the show being sophisticated is key, here. Game of Thrones (and Homeland) are not tat, but clever shows, aimed at a clever audience. McNutt reckons that's why sexposition has become a cultural meme: we're seeing the tactics of exploitation applied to shows that demand to be taken seriously, whereas no one would bat an eyelid were they not marketed as premium TV.

Deadwood – ready for another monologue? Photograph: 0NC/WENN

Sweet agrees. "In the 70s, when [cinema] producers had to be very aware of giving their audience the things they couldn't get on TV, producers would say to the writer: 'We need nudity and a murder before the titles.' The rules of screenwriting laid that down quite forcefully. You'd think HBO could be free of those diktats, but they-re not – they're giving you something that's not available on free-to-air TV. This is premium TV, but it gives you the same thrill that you got from 70s exploitation movies."

For some, though, sexposition is a diminution of the screenwriter's craft. "There's a great Hollywood saying," says Craig Warner, writer of TV dramas Britain's Greatest Codebreaker and Maxwell, among others. "'Breasts are still our cheapest special effect.'" He feels that a writer who needs to lay out huge chunks of detail in monologues or dialogues has usually failed. "I work hard to make sure there's no information that feels like it's just being given to the audience. Actually, I just never put in any expository material that one character doesn't need to tell another."

Will the second series of Game of Thrones still be awash with sex? Or will its producers recognise that we know sexposition when we see it? That point was put to executive producer David Benioff last year by the Daily Beast. Mary Whitehouse wouldn't have liked his answer: "We will address this issue with a 20-minute brothel scene involving a dozen whores, Mord the Jailer, a jackass, and a large honeycomb."

• Have you noticed any shameless sexposition in your favourite TV shows? Which do it well and which make you squirm?