Whirlpools are among the deadliest phenomena that bathers can encounter and are the underwater version of tornadoes.

They can drag swimmers at speeds of 15mph (24km/h), three times faster than many rip currents, and have been known to spin 120ft (37m) boats around. In cartoons they will drag people and ships deep into the water, as if a bath plug had been pulled from the seabed, but in reality they simply drag people around at speed.

The shape of the seabed at Tonel beach, the state of the tide, the waves, the curve of the shore and the position of a large rock near the end of the bay would all have contributed to the strength and direction of the currents.

Simon Boxall, of the National Oceanography Centre at the University of Southampton, said that once waves had crashed against the shore the water had to flow away. The physical boundaries and the shape of the end section of the bay meant that the currents flowing in and out were forced into narrow, fast-flowing channels and spun around in deadly eddies.

“You have these large waves coming in off the open Atlantic and these create rip currents,” Dr Boxall said. “The waves come in and that water has to go somewhere. You get lots of flows. Once you get caught in the maelstrom it’s very difficult to get out. With whirlpools you are looking at flows of 12-15 mph. In water, that’s very, very fast.”

He said that it sounded as if there had been an undercurrent which, because of the way it would drag at the lower bodies of swimmers, would have made it difficult or impossible to pull anyone in trouble to safety. “You have a huge weight of water — just one cubic metre of water weighs a tonne,” he added. “I’ve seen a 120ft boat in Svalbard \ being spun around by a whirlpool.”

Steve Wills, beach safety manager for the Royal National Lifeboat Institution, thought it likely that rip currents were involved in the tragedy. He said that the flag system on beaches in Britain, which was adopted as the international standard, should be used by bathers as a guide to where was safe to swim.

Anyone caught in a rip current is advised to remain calm and to swim parallel to the shore for a few yards to escape the fast-flowing water. Most bathers killed by rip currents drown because they exhaust themselves swimming against the flow.

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