Wearing only a pair of skimpy gold spandex shorts and a diamond studded Rolex, Bikram Choudhury, 60, sits enthroned behind an enormous ivory-inlaid desk in the office of his world headquarters in Beverly Hills. 'It's huge,' he says, 'I'm making - I don't know - millions of dollars a day, $10 million a month - who knows how much?'

His chair is covered with an orange and black tiger-striped towel which he sits upon as if in triumph. It reminds him of the wild animals roaming the forest around his native village in Bihar, one of India's poorest states. He lounges now beneath the framed photographs of movie star friends (Elizabeth Taylor, Shirley MacLaine), discussing his vast wealth and many talents; his long black hair flowing over naked, muscled shoulders. He has reason to feel astounded by his own good fortune, for although he sits here in Hollywood, at the epicentre of the brash new world that is capitalist America, Choudhury has made his millions from a 5,000 year-old Indian tradition promoting spiritual rather than worldly aspirations. He has made it in yoga.

He has 1,600 yoga studios around the world (up from 1,200 last year) from Texas to Tokyo, Bogota to Brighton and the brand name 'Bikram Yoga' has become the Starbucks of the yoga world. For 5,000 years, the practice of yoga has stood for a way of life involving Buddhist philosophy, a vegetarian diet and hours of meditation. Yoga has aspired to feelings of peace, wellbeing and 'oneness' with the universe. It may lead to lifestyle changes and painful self-analysis. However, yoga has also become the fitness exercise of choice in England and America and the attempt to expand the mind and link body to spirit, with its attendant navel-gazing and lentil bakes, is now outdated. Most shocking to the yoga purists, are the new versions of 'supermarket' yoga breaking into the market, including hip-hop yoga, disco yoga, online yoga, yoga with pets and even yoga for pets.

Choudhury was the first to spot yoga's enormous money-making potential, and in 2001 claimed copyright to 'his' 26-pose sequence and two breathing exercises - much to the fury of the wider yoga community, for whom claiming ownership of ancient asanas was tantamount to taking out intellectual property rights to verses of the Bible. This year, he says he has signed contracts with fitness corporations WorkOutWorld and California Fitness to franchise Bikram Yoga across the Far East, Japan and Asia. He expects to have 5,000 affiliated studios by 2008 and is in negotiations with another multinational wanting to buy franchising for China. Many fear that yoga is being hijacked as just another fitness exercise and its more esoteric elements eroded.

Halima Malik, deputy editor of Yoga Magazine says: 'If people want to look good and be fit, that's fine, but it's not yoga. The way yoga is being marketed, we're getting further away from the essence of it, which is spiritual, philosophical and ethical; it's not just about getting upside-down. But yoga is a great way of making money and everyone is cashing in on it.'

'Look at me,' Choudhury says, leaning back, with twinkling eyes. 'I have a lot of money now. We are doing yoga right now, you and me, we are exchanging our philosophy of life.'

Sheer cheek, energy and absence of self-doubt are the key to Choudhury's charisma and it is hard not to like him. He exudes happiness and is certainly enjoying himself. In fact, he likes to big it up: 'There's nothing like this in the world! Give me a pen or T-shirt and put "Bikram Yoga" on it and it will sell for $45.' He has developed a Bikram brand line in yoga clothing, jewellery, videos and even CD recordings of Choudhury singing songs he has written himself with lines like: 'I believe in God: it is me/I believe in yoga: it is the key' in Hindified English; accompanied by whining stringed instruments.

But his real hobby is cars: 'Look here!' (He points to a framed photograph on the wall of his office.) 'This is my favourite car. It is Howard Hughes's last limousine, his Royal Daimler, the only one in the world with a toilet inside.' He also loves his Phantom Black Cherry, which used to belong to the Queen Mother and a James Bond Aston Martin from the film Thunderball.

Choudhury has worked hard to get to sit on Howard Hughes's loo seat. His life story is a rags-to-riches drive for self-determination, reinvention and money. He was born in 1947 in Bihar, one of India's poorest states. He was a weightlifting champion in Calcutta at the age of 13, and when a knee injury halted this career Choudhury turned to yoga for a cure. 'By then, I looked like a baby gorilla: each leg was 26 inches wide and it took me eight months practising 20 hours a day to get my body down to size so that I could do the yoga.'

After becoming yoga champion of India at the age of 23, Choudhury decided to try his luck in America. He set up his first yoga studio in Los Angeles in 1973 and when actors began coming to his classes, he was dubbed 'guru to the stars'. Now there may be as many as 315 people in any one of his yoga classes, each paying £12 per session.

'Yes, 315 people!' he says delightedly, 'See how they love my yoga? It's fantastic! This is getting so big: yoga is an industry now, it is a business.' For Choudhury perhaps, there can be no higher accolade. But what about yoga as the ancient Sanskrit defines it: a bridge between body, mind and spirit?

Cramming as many students as possible into a class may be economic - but is it yoga? Bikram's sequence of 26 'hot' yoga poses and two breathing exercises - practised in a raging 105-degree temperature to mimic conditions in India - loosens up the muscles, sweat out toxins and effect weight loss. The exercise makes bodies very sleek, very fast. Michele Pernetta who runs three Bikram Yoga studios in London says: 'Bikram has tailored yoga to the Western market and stripped away the dogma: the bells, incense, props, mantras and hippy beads.'

Bikram yoga is turbo-charged, egocentric and extreme. It is confrontational and without mercy. Some say it is a mirror image of its creator's personality. When I question Choudhury about this, he leans across his huge desk towards me and raises an index finger. 'Your mind is your number one enemy. When you come to my class I guarantee you, for 90 minutes you will forget who you are, what is your name, whether you are man or woman, what you are doing here; for the first time since you were born your mind will be totally free, meditated from the rest of the world: I take you to another galaxy.' He has written a script, which teachers of Bikram yoga have to learn verbatim, so that the words used by them during a class are his alone. Choudhury's voice is supposed to bypass individual thinking and liberate the mind, but some resent the control he exerts. 'He's a dictator,' says one Bikram-trained teacher who asks not to be named. 'He works his employees to death and it's all about him getting really, really rich. To him it is strictly business and he demands total subservience.'

As yoga becomes more of a money-spinning exercise, traditional values like compassion, loving kindness and a disinterest in worldly goods appear to be lost. After living in Beverly Hills for 33 years, Choudhury's Indian-inflected monologue is full of cash quarrels, dropped names and - like his yoga - fast and furious, circulating a lot of heated air. Now, Choudhury couldn't be in finer shape: a lineless face, smooth muscled torso, strong thighs and the energy of a cobra ready to strike. And he has not held back from attacking anyone standing in his way.

In 2002, he sued Sandy McCauley when she attempted to set up her own independent school and the case was settled out of court. McCauley says: 'I question his right to copyright and to franchise yoga; it should be available to everyone. Bikram yoga is like eating a McDonald's burger; it doesn't mean you might not want to try pure Angus beef in a five-star restaurant sometime.'

Ex-students Dallas Kruzelnicki and Ali Hill also ran into trouble when they tried to open a yoga school in Brighton three years ago. 'We had our studio ready to open up, but Bikram said no - another student was given the Brighton affiliation. So we set up our studio under a different name, Yoga Haven.'

The partners have been ejected from the Bikram fold and labelled by him as 'imposters' running a 'Mickey Mouse organisation'. Choudhury argues: 'You can't drive a car without a licence. These illegals are using my name and diluting my yoga. I win every case: I put them out of business.'

There is a lot of money at stake. In 2004, the Wall Street Journal estimated the yoga industry to be worth $42 billion worldwide. Choudhury is delighted to say that this year yoga is worth $100bn. When I ask whether his yoga has sacrificed the traditional 'spiritual' aspirations, Choudhury frowns in irritation: 'What do people mean by spiritual? In 50 years of teaching, I have not met one person in the West who understands this word. It means self-realisation, it means how to realise your own spirit and how to use your body to reach and control your mind. When people cannot walk and they come into my class in a wheelchair, I make them stand and walk again. They go back home with smiling faces and they bless me and say Bikram, you saved my life, God bless you - that is the only food of my spiritual practice.'

He claims yoga can cure disease and even negate the need for food and sleep. 'Yoga is the petrol pump. My class gives you energy, like petrol for a car. I don't need to eat, I don't need to sleep. Americans are obsessed by diet. If your car engine is broken, does it make any difference how much petrol you put into it? If the body is not good, what difference is it what you eat? If the body is good, you can eat what you want.'

Mary Atwood, manageress at the Life Centre in London, says diet is an important part of yoga. 'Ayurvedic yogis believed that if the digestive system is healthy, even poison can be transformed into food, but we have to tailor ancient belief to the modern western world.' Katy Appleton, director of Apple Yoga in Clapham, says: 'Doing yoga does change eating habits, but you still need food, which is the body's fuel.'

While practitioners quibble about the best way to practise yoga, huge numbers of people are joining the Bikram boom. As his fitness empire grows, Bikram needs more teachers and the training course, which originally took four years, is now stripped down to just nine weeks. Tony Sanchez, an ex-student who broke from Bikram to set up his own school of yoga, believes that this is too short a time for a teacher to be responsible for their students. 'The teachers are not experienced and do not know enough to be able to modify the poses to individual needs.'

Choudhury says students are required to have practised his yoga for at least six months before applying to be a teacher. But the British Wheel of Yoga -the governing body for yoga in Britain - is already worried that teachers without adequate training are setting up studios in the UK. The organisation's chief executive Pier Bibby says: 'We are developing and regulating national standards. At the moment, anyone can say they are a yoga teacher and set up a school, and that situation is theoretically open to abuse.'

As far as Choudhury is concerned, teachers certified by him are the only legitimate ones allowed to teach Bikram yoga and increasing numbers of people want to qualify fast and start making money on the yoga circuit.

Choudhury laughs, as he reflects on how much the business has developed over the years: 'I used to grab people off the street saying "Come and be a yoga teacher!" Now, 700 people apply for each course and I accept only 200 or 250.'

When I joined prospective teachers at Bikram's West Hollywood studio last week, they were beginning their sixth week of training. Most are women aged between 20 and 35, though there are some men and a smattering of over-forties in the crowd. The totty factor is scorching: lithe young bodies braced in revealing sports bras and pants of Choudhury's own design: baby pink, blue, orange, red and definitely no green. (He says green is an unlucky colour and bans it from all his studios.)

In the lobby, an eight-foot high photograph of Choudhury seated on a tiger skin gazes down upon the uber-fit disciples who await their guru's presence in the flesh. He emerges from his office wearing a black silk suit, crepe silk shirt with pink-edged collar, black tie printed with garish gold diagonals and a feathered fedora. 'I designed it all myself,' he says and gamely climbs onto a pedestal for our photographer. There, he is surrounded by a selection of adoring and scantily clad babes, like a yogic version of Hugh Heffner. 'You are the king!' someone shouts and he grins at the lens; this is an asana (or pose) he appears particularly to enjoy.

Half an hour later, I join the class of 260 people gathered in a vast mirrored and carpeted studio, waiting to begin. This time, Choudhury enters the room wearing a tiny pair of black Speedos and with his hair tied in a topknot. He climbs onto a raised podium where he sits in an armchair and speaks through a headset. Each student has a litre of water, towel and yoga mat. We are reflected in the wall-length mirrors like a computer-generated army.

'OK shall we start?' 'Yes!' is the shouted response from everyone present. The first breathing exercise begins. The sound of mass inhaling and exhaling hisses like a human sea. Then the mirrored army lift arms over their heads and stretches sideways (half moon pose). Choudhury singles out a male student, pointing an index finger from the podium: 'Come on Mr Blue Pant, suck your stomach in. Why you have a fat arse, fat stomach, you been eating too much food?' Mr Blue Pant does not answer.

This is not a place for the sensitive. The poses have picturesque names like Locust, Rabbit, Eagle, Camel, but now the sight of normally hidden body parts exposed at awkward angles is testing. Sweat dribbles from body crevices fully opened and straining. The sound of Choudhury gulping down water echoes from the headset around the room's microphone system. 'Push!' he shouts, 'beyond your flexibility. More!' Someone's sweat sprays my bare arm.

Tendons extend easily in this heat and sweat drips off elbows and raised heels, pours down knees and backs. Choudhury appears to be oblivious of any discomfort among his students and now goes into diatribe about how he felt watching his wife Rajashree eating 'for two' when she was pregnant. (They have two children, a daughter aged 16 and son aged 13.) 'I got so disgusted to look at the way she ate, Jesus Christ, she put on 10 pounds and I took off 10 pounds.'

His general message is that people eat too much and 'yoga is food. Yoga is the fuel in the tank'. But it is hard not to notice that one teacher's body is emaciated, her hip-bones poking out like sticks. Clearly, this anti-food message could be taken too seriously by some.

But Choudhury has moved on. 'Bikram yoga is good for marathon sex!' he shouts. 'Once you do Bikram yoga you can't get it down for 72 hours!' Some manage to chortle, in spite of their contortions. 'The biggest problem in the Western world is divorce! Wind Removing Pose!' In response to this order, everyone lies on their backs with knees bent and pulled up into armpits. 'Why buy the cow if you don't get the milk? If a woman cannot do this posture don't think about getting married ... NO GAPS! If there is gap, instead of nice sex the man will be playing ping-pong under the bed, the husband loses his balls ... ' Some giggle, others frown in the effort of trying to work out what cows, ping-pong and gaps have to do with sexual congress. This monologue goes on, interjected with a little singing in Hindi ('My grandmother used to sing me this song') and more sounds of gurgling water as Choudhury slakes his thirst.

Below, his students are closing their gaps, gasping, groaning, some turning puce, eyes bulging, wet hair clinging to scalps. At last, he allows a short break - 'OK, I let you drink some water now, I'm being nice to you today' - and each student gratefully grabs for his or her litre bottle.

The discourse takes a new turn. 'I met Elvis Presley: he was a good friend of mine. If he did my class every day he'd be singing today. I sang for him, he laughed and he loved it!' Choudhury breaks into his own Bollywood version of 'Love Me Tender' , and then segues into 'I'm feeling lonely tonight ... la la la la la la la ... I forgot the words. Quincy Jones wanted to me to sing, but I said: No! He wanted me to sing rock'n'roll but I refused. I gave six songs to Michael Jackson ... '

The crowd respond like puppets for their master: limbs interlocking and bodies bowing before him at his command. They laugh at his jokes and when he sings a final song (ending his live rendition only when the recorded CD version is mixed onto the microphone system) they lie down flat on their backs like happy babies listening to a lullaby.

Later, after a shower, they emerge in the lobby again, smiling and shiny as cult converts. 'Fantastic!' says Tony Oostenbrink, 40, who is hoping soon to open his own studio in Vancouver. This exercise, in conditions of extreme heat, forces a heart-pumping, dizzying boost of blood and oxygen around the body. It induces a natural and addictive high. The endorphin rush is a roller-coaster.

But not everyone enjoys the Bikram yoga rush. I hear one student mutter on his mobile phone: 'He was bullshitting ... .' And according to Kundalini teacher Howard Davis, practising yoga at such high temperatures can lead to hyper-extension or dehydration. 'The other danger of working in such high temperatures is that people may want to drink too much before and after the class, and drinking too much water can cause kidney failure. In fact, you shouldn't drink any water while doing yoga, because it interferes with energy flow.'

Davis's yoga technique involves chanting, incense, the beating of a gong and chai (sweet tea) to relax his students. It is, in short, the antithesis of Choudhury's approach. 'Yoga was traditionally practised as a preparation for meditation,' he says. 'We close our eyes to focus on inner energy flowing through the chakras (power points). It is the interior life we are interested in, not the shallow outer world of illusion and body image.'

But Choudhury is indomitable: 'If someone comes to my class for the first time, I say: "Welcome to Bikram's torture chamber to kill yourself for the next 90 minutes".'

And his students seem more than happy to expand their earthly horizons. After qualifying in LA, they can travel to teach at any of his studios around the world. Samantha Lockwood, 24, says: 'This is like one big family, not just an organisation.' Later however, when Samantha performs the Camel pose for our photographer and Choudhury stands on top of her for what seems like too long, shouting: 'Take another one! She is dying!' I have to wonder what kind of 'family' this really is.

Robin Munro, director of the Yoga Therapy Centre in London, says: 'You should never push yourself beyond your limits. Commercialisation is taking yoga away from the deeper link between body and mind. We do gentle asanas, breathing and relaxation techniques; and we work on emotions and attitude. Yoga can provide useful tools for change by relieving stress and using awareness techniques to stop reinforcing stressful attitudes and lifestyles. The deeper philosophy of yoga is that we are all part of a whole. Just going out for yourself is not going to help anyone. There is a positive subversive element to yoga. The world does change through people's actions.'

The greatest change Choudhury has seen so far, has been to his own bank balance. Along the way, he has undoubtedly made a lot of his people very happy and very fit. How far this benefits the rest of the world remains to be seen.

How good is your guru?

Sophie Wilson offers a Who's Who of spiritual healing and wisdom

Deepak Chopra
Karmic Spirtualist

Past life
Spiritualist to the stars, he believes that mortality is an illusion. Demi Moore, left, is aiming to live to 130. He trained as an endocrinologist, then studied meditation in his native India.

A guru is born:
In 1993, Chopra appeared on Oprah to promote his book. Ageless Body, Timeless Mind became an bestseller. His 40 books have since sold over 20m copies worldwide.

Product
Output includes glossy erotic tome Chopra's Karma Sutra (Virgin, £20) and an Ayurvedic spa in New York. This year launched Virgin Comics with Richard Branson to promote Southeast Asian values.

Followers
Madonna will appear on his CD, Deepak and Friends. Other friends Prince Charles, Hillary Clinton and Mikhail Gorbachev don't - is he saving them for a podcast?.

Princess Diana moment
He lunched with Diana shortly before her death. Don't tell Demi.

Repeat after me
'The way you think/eat/behave can influence your life by 30 years.'

Nishi Joshi
Holistic detoxer

Past life
BA steward turned osteopath and diet guru. From his London clinic, Joshi offers Ayurvedic medicine and homoeopathy to achieve 'an inner and outer glow'. Born in Tanzania to Indian parents.

A guru is born:
He 'cupped' Gywneth Paltrow's back. He gave Kate Moss acupuncture, but Kylie went on the record to say he wasn't treating her for cancer.

Product
Dr Joshi's Holistic Detox (Hodder Mobius, £12.99) was the hit of last summer. His new book, Joshi's Holistic Life Plan (Hodder Mobius, £12.99), drops 'doctor' because he's actually an osteopath.

Followers
His Primrose Hill-skewing client list includes Kate Moss, Sadie Frost, Gwyneth Paltrow, Cate Blanchett, Patsy Kensit and Ralph Fiennes.

Princess Diana moment
Diana gave him an Asprey wallet for his birthday.

Repeat after me
'If no one says how great you look you must be cheating.'

Tony Robbins
Neuro-linguistic life coach

Past life
The most successful motivational speaker, said to earn $80m a year. His books have been described as 'plastic surgery for the mind'. A former janitor and rumoured Presidential candidate for 2008.

A guru is born:
Robbins brought neuro-linguistic programming (NLP) techniques to the masses with Men Are From Mars, Women Are From Venus author John Gray as his support act.

Product
At his four-day Unleash the Power Within seminars, in London, participants firewalk on hot coals in bare feet. Books include Unlimited Power and Awaken the Giant Within.

Followers
Has advised political big guns Mikhail Gorbachev, George Bush Sr and Bill Clinton. Plus political big pecs Arnold Schwarzenegger.

Princess Diana moment
He met Diana. She didn't firewalk...

Repeat after me
'We can change our lives. We can be exactly what we wish.'

Sharon Gannon
Animal-rights yogini

Past life
Gannon aka Tripura Sundari is co-founder of the Jivamukti Yoga Method, a spiritual form of high-energy hatha yoga. Big hit with NY's arty set. Has schools in Munich, Toronto, Detroit and London.

A guru is born:
After boho beginnings as a jazz singer/choreographer, Gannon upped her profile in 2003 when she appeared on a Times Square billboard advocating yoga as a route to world peace.

Product
Co-writer of two books, translated a book of chants and penned petfood expose Cats and Dogs Are People Too! (Jivamukti Yoga Center, $15.95) Eco projects include a wildlife park in upstate New York.

Followers
Sting plucked his sitar at the opening of New York's Jivamukti centre while his wife lectured on the evils of cappucino. Other fans include Donna Karan and Uma Thurman.

Princess Diana moment
None on record, does Trudie Styler count?

Repeat after me
'Sarva mangala-mangalye shive-sarvatha-sadhike...'

Eckhart Tolle
'Be here now' mystic

Past life
Born Ulrich Tolle in Germany in 1948 - he dreamt the name 'Eckhart' - this Cambridge-educated mystic has earned more than £6m from his books. He advises followers to 'be' rather than to 'think'.

A guru is born:
At 29, Tolle underwent a spiritual rebirth shedding his old identity. He joined a Buddhist monastery, preached at Glastonbury and moved to, where else, California.

Product
His 1997 self-help manual The Power of Now (Hodder, £7.99) sold millions. Follow-ups Stillness Speaks (Hodder Mobius. £7.99) and A New Earth: Awakening to Your Life's Purpose Michael Joseph, £14.99).

Followers
Tolle's dolls include Gillian Anderson, Oprah, Cher and Meg Ryan.

Princess Diana moment
Well, he does have a home in Kensington.

Repeat after me
'Reincarnation doesn't help you if you are in your next incarnation ...'

· For a list of certified Bikram Yoga studios in the UK see www.bikramyogauk.net