A British endurance athlete is going for a world record for a one-kilometre swim in water so icy it normally kills in minutes.

Lewis Pugh, 35, whose unique capacity to withstand the cold has attracted the attention of scientists, was expected to take about 22 minutes to complete the swim in the Southern Ocean near the Ukrainian scientific base of Vernadsky.

At 65 degrees south, it is the most southern swim attempted, and could break the world record held by the American swimmer, Lynn Cox, since 2002. Pugh will be the first person to have swum in both the Arctic and Southern Oceans.

The temperature of the water where he will swim has a temperature of 0C (saltwater freezes at minus 1.8C), cold enough to disable most ordinary mortals instantly.

In the UK, the average swimming pool temperature is about 27C, and the English Channel , which most people would find distinctly chilly, is 17C to 18C. Cold shock is the normal reaction on being suddenly immersed in icy water, causing involuntary gasping for air and rapid loss of muscular control and co-ordination. Drowning may follow.

Through training, Pugh has overcome these responses and schooled his body to generate extra heat. His training regime involved regular dips in an ice-filled pool and he has spent years performing lengthy cold-water swims.

Four months ago he broke the world record for the most northern swim when he completed a one- kilometre course around Verlegenhuken, 1,100km (684 miles) from the North Pole. In Norway, he swam 204km (127 miles) down a fjord, which so impressed sceptical locals they awarded him the title "Ice Bear", He is also the first person to have swum across an African great lake, Lake Malawi.

Pugh was born in Britain in 1970 but moved from Plymouth with his family to South Africa when he was 10. His father was a surgeon in the Royal Navy and he was raised on a steady diet of adventure stories. He read law at the University of Cape Town and Jesus College Cambridge and has a second career as a polar adventurer and endurance swimmer.

In an interview with The Lancet medical journal, in its medicine and sport supplement, he said his body has adapted physiologically to the cold.

As soon as he sees icy water, his temperature rockets to 38C, well above normal. Studies have shown that it takes professional cyclists 20 to 30 minutes to reach this temperature in competition. "My body realises it is going to get cold and so it turns on the burners," he said.

Professor Tim Noakes, head of sports medicine at the University of Cape Town and one of three scientists who accompanied Pugh to Antarctica, has called his response "anticipatory thermogenesis", a Pavlovian reaction which leads to the creation of heat before he dives into the water.

During his Arctic swim, Pugh lost one degree of his core body temperature for every 10 minutes he was in the water, so starting at 38C helped him complete the attempt.

He said: "I never do the same swim twice, unless for training. The next swim must be harder and more challenging, otherwise I am going backwards."