The invention was tested in the Lake District

Keen swimmer Peter Hayes, from Beamish, found police had taken away his clothes during a day at the beach, believing they belonged to a suicide victim.

It was a scene similar to the popular TV series the Fall and Rise of Reginald Perrin, in which a man leaves his clothes on a beach feigning suicide.

Mr Hayes has come up with a waterproof rucksack, which he can take swimming.

The 41-year-old university politics lecturer says he is eager to avoid a similar incident and let the police deal with more serious matters.

Waterproof layer

His solution is the Swimsac, a rucksack with a waterproof compartment, which he claims keeps its contents dry even in the deepest water.

Mr Hayes says 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.

To compensate for the added weight of boots, clothes and towels, he has included two inflatable pouches that can be blown up in seconds to increase buoyancy.

Mr Hayes, who spent five years developing the product, which it hopes will go into production soon, said: "The outer layer of the rucksack leaks, which makes it more comfortable to wear both in and out of the water.

"It is the waterproof inner layer that keeps things dry.

"We tested it in the Lake District in summer and off the coast of Scarborough in winter."