On Wednesday six pupils from King's High and Warwick School joined forces in a relay from Shakespeare Beach in Dover to Cape Gris Nez in France, while another team of seven were due to set off around 8am this morning (Friday).

Speaking ahead of the challenge, Warwick School Maths and IT teacher Peter Nield, who has been training the teenagers, said: "We're ready now. You could always have another two months of practice, but they are at a peak and if they don't go now, they might get too nervous."

Mr Nield, who swam the Channel solo in 1994 in 11 hours and 58 minutes, has been leading training sessions since October, and for the past few months the 13 to 18-year-olds have been swiming in lakes to prepare their bodies for the cold.

He said: "Some of the girls and boys have found it very difficult to cope with the cold because they don't have enough body fat to take it.

"We have had to advise some that they should not do it or else they may get hypothermia.

"Others have taken to it like ducks to water."

The swimmers are hoping to raise £10,000 for Acorns Children's Hospice.

Contending with water temperatures as low as 14 degrees centigrade, the pupils swam in relays of one hour and obeyed strict rules of having to wear standard swimming costumes, goggles and hats.

Mr Nield said: "There are so many hazards we cannot take account of.

"The tide and the water can change, supertankers going past could generate enormous waves and if it is raining heavily you cannot see anything.

"Then there are the dangers of jellyfish, seaweed banks, people getting cramps or seasickness and a great many more I won't mention."

He added: "It's very exciting but very daunting. In some ways it's terrifying, in others it's the greatest thing you can do."

Anyone wishing to sponsor the teams can do so by visiting www.justgiving.org/warwickschoolswiming or calling the school on 776400.