And as the eight canoeists on a team-building exercise tried to escape the freezing water on to a support boat, it also capsized, sending the phone - the group's only form of communication - into the harbour depths.

Two instructors on the 12ft fibre-glass boat also fell into the water.

By chance a passing barge rescued the 10 stranded men and women. The eight British employees of Danish shipping giant Maersk were taking part in a management training course at Brenscombe Outdoor Centre at Corfe Castle.

They set out on April 6 morning in two Canadian kayaks, accompanied by a support boat, and were between Brownsea Island and Furzey Island when disaster struck.

With gusting wind whipping up the waves the kayaks sank.

Once in the water the eight tried to clamber on a support boat nearby, but this also capsized.

"They called their company on a mobile phone to get more rescue support boats to come out," said Mark Cole, second coxswain on the RNLI Poole offshore lifeboat.

"Fortunately the Furzey Island transport barge was passing and picked them up. When we arrived they were transferred to the lifeboat. They were all very cold and some were having asthmatic attacks."

Commenting on the support boat that accompanied the kayaks, Andrew Jenkins, of Portland coastguard, said: "There was no radio or flares onboard, and this vessel also rolled over losing their only form of communication when they were trying to pull people onboard.

"It seems they had tried to instigate their own rescue by phoning their local office and rescue boats would have gone out from Ridge Wharf which was at least an hour away."

The accident happened just before 1am on Saturday when the silver Mitsubishi Lancer was travelling north along the A350 Holes Bay Road and left the highway just north of the junction with Sterte Road West.

Three local men and two local women, whose names and ages have not been released by police but who are thought to be in their 20s, were travelling in the car.

Firefighters waded into the water to rescue four of the casualties, but the RNLI was called out to help them search the muddy water for the final male passenger.

Gavin McGuinness, helmsman of the inshore lifeboat, said that as he and two colleagues arrived at the scene, they could see four wheels sticking out of the water. "The fire brigade believed there was nobody in the car and asked us to do a search of the water," he said.

"We located a gentleman who was about a foot under the water, face down. I entered the water and pulled him to the surface and dragged him towards the shore, where two firefighters met him and we carried him to the paramedics."

He added that the man, who seemed to be in his early 20s, had a gash to his head and did not appear to be breathing.

Paramedics tried to resuscitate the man, and took him to Poole Hospital, where he was pronounced dead.

The other passengers were also seriously injured and the male driver escaped with slight injuries.

Dorset Police, who closed the road off until around 10am on Saturday, are appealing for witnesses to the accident and anyone with information to call the road policing unit at Ferndown on 01202 222222.