Free Diving: With one breath, the world's most perfect athlete dives 122m to break all records

"We all have a common physiology with dolphins and it is just a matter of how you harness that."

So said Tanya Streeter yesterday. The 30-year-old former Roedean pupil and graduate of Brighton University had just dived to a record-breaking depth of 400 feet (122 metres) with the aid of a single breath which had to sustain her for almost four minutes under water.

In doing so, she became the first person - man or woman - to break all four freediving records with her latest feat in the "variable ballast" category, which requires the diver to swim back to the surface instead of being pulled.

The International Association for the Development of Apnoea, one of the sport's governing bodies, promptly declared that she had shattered the previous women's record of 312 feet (93.6 meters), by Mandy-Rae Cruickshank, of Canada, and beaten the men's record too.

She is already hailed in America as the "world's most perfect athlete", with a pair of lungs that defy medical convention (she can actually hold her breath for six minutes). Now her achievement - in the cobalt oceans off the Turks and Caicos Islands - may finally earn her recognition in the country where she was raised.

Speaking to The Independent shortly after surfacing, she said: "When I got the surface I wanted to scream with delight but I couldn't in case I passed out, which would have disqualified me.

"I had to keep my mind on the rules - thumbs up to the judges and then wait a minute without touching anyone. After that we all went crazy - kissing, hugging and splashing."

Freediving, the oldest extreme sport in the world, became a competitive event 55 years ago and is now practised in waters from Bulgaria to Portsmouth. There are 20,000 registered divers, but Ms Streeter is considered the best.

She insists that she has reached the top through sheer determination rather than inherited physiology. "I liken it to sprinting - we are all capable of that but only a few have the ability to get under 10 seconds.

"Through endeavour I have managed to redefine what the human being can do. A dive is 95 per cent in the mind. I didn't switch on until just after I went under. I'd only just gone down when I saw a dolphin and said to myself, 'Today's going to be a good day.'"

Yesterday's dive was an object lesson in following her mantra: determination, preparation and concentration. Wearing fins, a nose clip and a wetsuit, she descended into the azure depths about a mile and a halfoff the west coast of the island of Providenciales at a spot where the sea is about 7,000 feet (2,100 meters) deep.

Using a 200lb weighted sled, she dropped along a line dangled from a boat, and passed six safety divers spread out along the line. Two other divers using special breathing equipment waited at the bottom of the rope and for encouragement sang Elton John's "Crocodile Rock", which had became a theme song during her three months training.

She kicked her way back to the surface, emerging after three minutes and 58 seconds, giving two thumbs up before swimming back to the boat.

Her husband, Paul Streeter, who had dived down to about 60 feet (18 meters) and followed her up, surfaced right behind her. Then they embraced and Ms Streeter pumped her fists in the air.

That Ms Streeter could speak at all was some achievement considering the strain the dive would have placed on her body. During a previous dive to 160 metres she described the symptoms of deep-water pressure: eardrums feeling like they are being speared with pokers; thoughts of blacking out, oxygen starvation that nearly stalls the heart and strains on the chest wall to the point approaching implosion under 11 times the pressure felt at sea level.

But she has been there before. Ms Streeter has held a total of eight world records. The other three women's categories in which she has reigned supreme are the "no-limits" section to a depth of 525 feet; "constant ballast" (229.7 feet) and "free immersion". The depth of the record achieved reflects the amount of assistance the diver receives from guide ropes or pulleys on the way up or down.

Although it is the original extreme sport, freediving has been suffering an image problem since the death last year of the French woman Audrey Mestre, 30, who drowned in the waters off the Dominic Republic while trying to break Ms Streeter's 160-metres record in the "no limits" category, which involves being pulled to the surface by an inflatable airbag.

As the sport's most famous ambassador Ms Streeter said she found it "abhorrent" that anyone would risk their life for a world record. Fearing that she would struggle to cope with the pressure change, she spent hours before the descent "packing" her lungs: taking in deep breaths to equalise the sea's pressure in her airways. During her descent an unprecedented 15 safety divers were stationed at strategic points, including two freedivers on the surface, and advanced underwater communications were used. "Safety is important for the credibility of the sport. It's not just about me but everyone else," she said. "When the dive was over I swam down to the safety divers to give them a bottle of champagne."

Speaking before the dive she told one reporter: "It's harder to dive because the ascent is made unaided. So it's a combination of pulling yourself up the rope and kicking like mad. The depth isn't as deep as the no-limits but it requires considerable physical strength, which means the men have a distinct advantage. I don't set out to break a man's record, I just want to extend my own limits."

Ms Streeter said she was already a "child of the sea" when she emigrated with her mother from the Cayman islands - where she spent hours swimming and snorkelling - to England in the 1960s.

Her excellence at sport was nurtured at Roedean School in West Sussex and she went on to study public administration and French at Brighton University, where she met her husband, Paul, who was born in Brighton.

Because of a shared love of watersports they moved to the Caribbean and then to Austin, Texas, two years ago to secure big-name sponsors. Her latest dive, for which she has been in training for three months, cost around £47,000 paid for by her sponsors Tag Heuer (she wore the 2000 Aquagraph for yesterday's dive), Red Bull and the Turks and Caicos Tourist Board.

With her ambition, athleticism, the looks of a swimsuit model and business savvy Ms Streeter has spawned a mini extreme sports industry. Yesterday's events were recorded with underwater cameras for a documentary on Dateline NBC to rank alongside her numerous appearances on the National Geographic channel.

Such is her status in the Turks and Caicos islands, where most of her record-making dives have been held, that she was honoured with a set of stamps from the former British colony, thereby becoming one of the few living people to feature on stamps bearing the Queen's head.

After collecting the latest record, she plans to use her status as a celebrity to aid the conservation of the environment as a leading member of the Coral Reef Alliance and the Whale and Dolphin Conservation Society.

"At the current rate of erosion my grandchildren won't get to see a coral reef and that would be a great pity. Not that I have any children of my own yet - that may be my next goal," she said.

Free Diving: The physical risks

The extreme sport of freediving places enormous strain on the human body, pushing it beyond its normal limits and running the risk of serious injury and even death.

As Tanya Streeter began her descent to 400 feet (122 metres) her lungs would have started to compress - just 10 metres below the surface their capacity would already have been halved and at 30 metres they would be only a quarter of their original size. By the time she reached the record depth they would be crushed to the size of small fists, and her heart rate would have slowed to 15 beats a minute.

"The lungs in effect start to collapse," said Jim Watson, coaching and instructor training scheme manager at the British Sub-Aqua Club.

Ms Streeter is capable of holding her breath for more than six minutes - a state known as apnoea - but the compression of the lungs reduces their surface area and hence the transfer of oxygen to the bloodstream. This can result in starvation of oxygen to the brain, unconsciousness and possible drowning.

Other problems are the light-headedness caused by the high concentration of carbon dioxide in the blood stream, partial crippling of the legs and intense pressure within the inner ear. Freedivers have to force air from their lungs and throat into their ear canals - for example by pinching their nose - to prevent rupture of the drums. The process puts immense pressure on the sinuses.

As the freediver resurfaces the lungs should gradually expand back to their usual capacity, but there is a danger that the inside walls may touch each other and stick together.

The key to a successful attempt is Ms Streeter's ability to expand her lungs far beyond their typical volume before she descends, and her ability to slow her metabolic rate to prolong her limited oxygen supply.

By Oliver Duff