By COLIN FERNANDEZ

Last updated at 00:09 21 July 2007

Only a few seconds in the icy depths would be enough to kill most mere mortals.

But yesterday, protected by nothing more than a pair of Speedo trunks and his extraordinary central heating, Lewis Pugh took the plunge and became the first man to swim at the North Pole.

The 36-year-old Londoner spent almost 19 minutes at minus 1.8C as he front crawled for a full kilometre - more than half a mile in the coldest water a human has ever swum.

Amazing video: Watch Lewis training for his world record attempt here

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"It was like jumping into a dark black hole," he said. "The pain was immediate and felt like my body was on fire.

"I was in excruciating pain from beginning to end and I nearly quit on a few occasions. It was without doubt the hardest swim of my life."

But he said that a colleague ski-ing on pack ice alongside him looking out for hungry polar bears spurred him on.

"I just kept on looking at Jorgen Amundsen ski-ing next to me, encouraging me. I will never ever give up in front of a Norwegian! Let alone a relative of Roald Amundsen (who beat Britain's Captain Scott to the South Pole.) There is just too much rivalry between our two nations for that."

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Pugh, who gave up his career as a maritime lawyer to become a full-time endurance swimmer, carried out his latest expedition to highlight how global warming has melted the Arctic ice- caps.

He travelled to the geographic North Pole on a Russian icebreaker with a 29- strong back-up team including a mind coach.

To develop his cold sea swimming technique he practised in a pool filled every day with a ton and a half of ice.

He has broken more than 20 endurance swimming records which include the first swim of more than 1km in the Antarctic Ocean.

He has swum the whole of the Thames, been first to swim the length of the world's longest fjord and first to swim round the most northerly point of Europe.

He is also the first man to swim at the South Pole - where the waters are a comparatively warm zero celsius.

Although the North Pole temperature is below zero, the salt is enough to prevent the water freezing at that temperature.

Pugh carries out his swims to Channel Swimming Club rules - which outlaw wetsuits, flippers or snorkels.

He chooses not to cover himself in goose grease as he does not want to be too slippery for his team to fish him out of the water in case he develops hypothermia.

• Lewis Pugh's incredible ability to withstand the icy cold has been developed over years of training.

Before he dives in, he spends around 15 minutes using mind power alone to superheat his body.

His pulse rate shoots up from 70 to 160 a minute and his temperature rises from 37C to 38.4, causing him to sweat profusely.

This is all without moving a muscle - and something which would take an ordinary person around 30 minutes of hard exercise to achieve.

He also plays aggressive rap music - Eminem is a particular favourite.

Describing the feeling of swimming in water more suited to seals, whales and polar bears, he said: "Before I get in, my body feels like a furnace. I become very aggressive, and my surroundings seem to slow down. Then I hurl myself in.

"At first, you experience massive hyperventilation. Controlling this is extremely difficult."

On leaving the water yesterday, his core body temperature had fallen to 36.5 degrees and it dropped further to 35 degrees 20 minutes later but a warm shower enabled him to return to normal.