IT was one of those moments of pure embarrassment.

Peter Hayes returned to the beach after a long swim to discover police, thinking that he had committed suicide, had taken his clothes away. To add insult to injury, he had to walk miles into town in his wetsuit with children behind him chanting "quack quack".

The misunderstanding, coupled with inspiration from the ancients, led the university lecturer to come up with an invention that would allow him to take his clothes with him on swims and let the police deal with more serious matters.

His solution is the Swimsac - a rucksack with a waterproof compartment, guaranteed to keep its contents dry even in the deepest water.

Dr Hayes, who works at Sunderland University, said: "I had gone for a really long swim from a beach in Sunderland and returned to find my rucksack with my clothes and keys had been taken.

"An elderly couple told me there had been a suicide and police had taken it away - I had to convince them I had not killed myself."

Dr Hayes, 41, of Beamish, County Durham, said he was inspired by a 3,000-year-old Assyrian stone panel he saw in the British Museum showing men floating in water holding on to inflated goatskins.

The outer layer of a Swimsac leaks, which makes it more comfortable to wear both in and out of the water. A waterproof inner layer keeps things dry.

The design's durability has been tested in the Lake District in summer and off the coast of Scarborough in winter. Peter spent five years getting the design right and patenting his version.

He has prepared a booklet giving instructions on how to convert an ordinary rucksack into a Swimsac in one evening and plans to sell the guide for £3.50. For more information, visit www.swimsac.co.uk