Being naked in front of a classroom is something most of us will only ever experience in our worst nightmares. Yet here I am about to embark on a Naked Yoga class with people who have paid good money to bare it all in a room full of strangers.

In a dimly lit studio in south-west London, we undress in the shadows before practising a couple of hours of meditative yoga in silence with eyes mercifully closed, before we slink back into our clothes and leave without uttering a word.

A big element of naked yoga, I'm told, is getting over body hang-ups and increasing confidence. Speaking to people who teach it and practise it, it sounds like an intensive form of psychotherapy.

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Naked yoga is a critique of consumerism, which says that when we strip down, we're all the same. Designer yoga gym shorts won't save you. Here, your body – or perhaps your soul – is the only currency that counts.

"There have been women that have come that have had body issues, problems with their weight, who have felt like they have benefited from coming to the classes in a big way," says Annette, yoga instructor at Naked Yoga London, who also teaches the class naked.

"It's that thing of overcoming one of your greatest fears and being OK with it, and being, like, 'It's not there anymore, that thing that was holding me back. I've gone beyond it now. I've triumphed over it.'"

The practice of naked yoga, or "nagna" yoga, has been around since ancient times and is still practised by religious figures in India. In the 1960s, it became popular among followers of the hippie movement in the US. And now it's making a splash due to mixed-gender classes becoming popular in cities such as New York and LA.

In London, it's still very much a man's club, with all-male classes run by YogaNu and Altogether Yoga in London. Annette's mixed-gender class at Naked Yoga London is the only one of its kind in the whole of the UK.

Nudity isn't essential at Naked Yoga London, unlike at some other centres, but Annette recommends it because it expands the basic principles of yoga by encouraging a deep acceptance, or "aparigraha", of ourselves and others. The more squeamish are encouraged to strip down to a sarong until they feel comfortable taking it off. Mine stayed firmly in place all night.

I'm trying to get to the bottom of why a woman would want to bare it all, when Grace Lenhart, 21, a regular at Naked Yoga London, explains that she does it as part of a New Year's Resolution to "love herself more".

"I feel stronger as a person when I'm doing naked yoga because I'm doing an extra thing of being naked, which is vulnerability, but once you push through it then it's a strength," says the religious studies student from Wisconsin.

It's not always a confidence-building exercise. Some claim that they find naked yoga relaxing. After experiencing it myself, there really is no better way to explain it, but I imagine it was very much like this in the womb. Soft red lighting and candles emanate warmth, while a comforting smell of incense, mixed with meditation music, trails the air. Someone, somewhere, starts to snore. Annette's soothing voice lifts and falls as she guides us through the postures.

Grown adults, naked as the day they were born, curl up on their towel-covered yoga mats into the "Balsana" or child's pose. It's like a return to a childlike state, when nudity is just a natural state of being.

The Dynamic Yoga Method practised at Naked Yoga London is a very individual experience of seeing but not touching.

Not true in the all-male camp, says Richard George, instructor at all-male naked yoga centre YogaNu in London. "There is almost always an element of touch involved. I think that's quite interesting in itself, because people crave touch, a lot of people. Whether that's from childhood or just the fact that they're single people, I'm not sure."

Meanwhile, on an emotional level, he says: "I've had people emailing me saying, 'I've built up the courage to come to class', then they get there, they get all the way to the door and then have just gone home because they're too scared. That's how deep the hang-up is within some people. That's why it's like a therapy."

My naked yoga class seems to be over when it's only just begun, ending with a 15-minute long "Savasana", or wind-down phase, in which Annette circles the room covering everyone up with blankets unless – like nudity-challenged moi – you're still wearing your cover-up.

Throwing off shackles of consumerism in a flash of naked yoga therapy might be liberating for some. As admirable as it sounds, it proved a step too far for me.

A course of four, 1 hour 45 minute sessions at Naked Yoga London costs £75 and is suitable for all levels.

nakedyogalondon.co.uk