Guests wander the luxury Mayfair apartment in formal attire, chit-chatting, lounging on sofas and sipping champagne. At midnight a bell is rung and everyone gets naked. Around half an hour later, after the initial awkwardness has worn off, the flat is a sea of writhing bodies.

Heaven Circle, probably the world's biggest sex party club (it's the one from that Channel 4 doc Sex Party Secrets you may remember), started out in 2012 as founder Chris Reynolds Gordon and just a handful of friends. Four years later, it has over 20,000 members, with parties taking place in London, Paris, New York, L.A., Vegas, Ibiza, Berlin, Amsterdam and Vienna. They always sell out.

The parties are hugely opulent, a recent one having taken place in a £30 million house in Marylebone. "How do you find the venues?" I ask Gordon. "I live in them," he tells me, which demonstrates pretty well how lucrative a business it is and the enormity of the world's sexual appetite.

If you're going to have sex with a total stranger, you're probably going to want them to be attractive, so Heaven Circle vets its guests, even operating a tiering system with extra special parties for the sexual elite. A "sex olympics" is currently being planned, where the best performers from parties around the world will come together for a sort of fantasy team orgy. The mix at the parties tends to be mostly swinging couples, with a few single men and women thrown in too.

A 'playroom' before a party

While the prospect of having so many sexual encounters in one go might frighten some, the organisers believe the parties to be safer than clubs. While the latter are plagued with unwanted gropes, the former is a less ambiguous environment. Everyone knows why they're there.

Consent is also held in paramount importance, with undercover bodyguards at all parties (wearing Y-fronts and bow ties, the best kind of disguise).

"I go to some of the best clubs in London and I find my parties are just friendlier," Gordon says. "I mean, if you're about to f*** someone's wife, you've got to be pretty friendly.

"In a normal club people are often a bit hostile, show off-y, they like to keep themselves to themselves. There's not that kind of 'Hey, how are you?' - just randomly chatting to people - that we have.

While Heaven Circle is a secret indulgence for most members, it seems that in an increasingly sex positive age where dating and hook-up apps like Tinder are ubiquitous, this embarassment is fast eroding.

"70 or 80 per cent of our members use photos of their face," Gordon explains, "you would never have got that before. It used to be pictures of, like, an arse bending over, now their photos are all them. They don't give a f*** - even in the workplace, people will say 'yeah I went to an orgy' and the response will be 'ah, cool.' It's not even taboo anymore.

Iconic sex scenes Show all 11 1 /11 Iconic sex scenes Iconic sex scenes Basic Instinct Sharon Stone and Michael Douglas in Basic Instinct, famous for its graphic sex scenes and infamous 'leg-crossing' scene Rex Iconic sex scenes Titanic Leonardo DiCaprio's hand in his Titanic sex scene with Kate Winslet is iconic in itself Iconic sex scenes Dirty Dancing Jennifer Grey and Patrick Swayze dance to Solomon Burke's 'Cry To Me' in the Dirty Dancing sex scene Iconic sex scenes Bridget Jones' Diary The 'absolutely enormous panties' moment between Bridget and Daniel Cleaver in Bridget Jones Diary Rex Iconic sex scenes When Harry Met Sally Meg Ryan faking an orgasm in the middle of a packed diner as Sally in 1989's When Harry Met Sally Iconic sex scenes American Beauty Lester is enchanted by his daughter's best friend (Mena Suvari) in American Beauty Iconic sex scenes Ghost Patrick Swayze and Demi Moore's sex scene takes place at a pottery wheel REX Iconic sex scenes Atonement James McAvoy and Keira Knightley steam up the library in 2007's period romance Atonement Iconic sex scenes The Sessions Helen Hunt having sex with a severely disabled man who's never had sex before in The Sessions Iconic sex scenes Hot Shots! Charlie Sheen cracks an egg onto the stomach of love interest Valeria Golina in the 1991 spoof Hot Shots! Golina is so 'hot' the egg fries straight away and Sheen's character decides to add some bacon Iconic sex scenes Fifty Shades of Grey Not so much one iconic sex scene as a whole movie full of them, Dakota Johnson and Jamie Dornan play Anastasia Steele and BDSM-loving billionaire in the big screen adaptation of EL James' erotic novels - prepare to get hot under the collar (while sporadically breaking into fits of giggles)

"I remember about 10 years ago when Plenty Of Fish came out people wouldn't want to talk about it, they felt only 'weird' people go on those kinds of services. Now it's so mainstream, people are screenshotting Tinder and showing their friends."

The company's next step is Heaven Prive, which will see it facilitate members setting up their own parties, potentially creating an explosion of orgies in countless other towns and cities.

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