The lilting beat of "Don't Worry, Be Happy" sets the tone. Green and red scatter cushions fill the floor and nervous strangers sit around awkwardly, preparing to get up close and personal at a "cuddle workshop".
Organiser Anna Nathan announces the rules in a comforting voice.
"You don't have to do anything you don't want to do," the 36-year-old tells the two dozen men and women sat round in a circle in a dance studio in north London.
"Keep a layer of clothes on. Place your sexual energy to one side. No kissing."
Today's students include a recently divorced 30-something "in need of a hug", some long-term singletons, a young man who's "very annoyed" with his girlfriend, and a retired man -- who are all about to get to know each other much better.
The room is cool, and apart from one or two people in T-shirts, the participants are all wrapped up warm.
Exercise one: walk around in time to the music, clicking your fingers, and get to know people by briefly touching their fingers, shoulders, feet, ears and finally their hips.
The first moves are hesitant, but laughter quickly erupts, breaking the tension.
Over the next four hours, Nathan and her co-host Neil Urquhart, 42, divide the class first into pairs, then small groups, and guide them through stroking each other all over their body, torso and pelvic area excluded.
"At some point, I was like: wait, I am just cuddling someone I just met," said Bailey, a 20-year-old American student.
"In any other place this would be weird. But because we are coming to a workshop, it's fine."
She admitted to being surprised at finding such a class in London -- "if I expected this type of thing to be anywhere, it's in California, with some hippies."
For the final exercise, the small groups break up and everyone is asked to lie down together on the floor, where they touch and hold each other -- while still respecting the rules.
"I feel really relaxed. I likened it to taking ecstasy tablets. It reminds me of that experience," confessed one euphoric cuddler, Grace.
The workshop, which costs £29 (over R400) for a session and takes place about twice a month on a Sunday afternoon, is not met with exclusively positive reactions.
"Some guy had a really freshly laundered shirt, and I was like, 'that's nice, that's so comforting'," said Bailey.
"But the next person, I was like 'noooo, that's not that comforting, you could have tried better, come on!' And I was like: 'Oh my God, I hope I don't smell'."
Participants are advised beforehand to avoid wearing strong perfume or aftershave.
The inevitable concern about such workshops is they might attract people wanting more than an innocent cuddle.
But Nathan and Urquhart keep a watchful eye on the proceedings, and they insist they have only had to intervene a few times since the workshops started two years ago.
"We've never had to separate people or pull them apart," said Urquhart.
The aim of the workshop, similar to the cuddle parties that have taken off in the United States, is to provide some comfort in a society where social interaction increasingly takes place via telephone or a computer screen.
Returning to the outside world is a jolt, but the organisers soften the blow by arranging for those who want to have dinner together nearby.
"If I had to go straight to the street and public transport, I would feel kind of cold and alone," said Andrew, a single man aged 42 with 10 workshops under his belt. "I want to hug everybody I see, if they are going my way or not."
Dinner also offers participants a chance to arrange to meet people they have met at the workshop for more cuddles -- this time perhaps with no rules.