Gwyn Sullivan shows the blanket to John Read, of Thermal Solutions

Gwyn Sullivan, 66, had the idea when his son was given a foil survival sheet to keep him warm after a marathon.

He believes not only will the blanket both warm and cool patients, the agent stops any bacteria surviving on it.

Mr Sullivan hopes his invention will be accepted by the Department of Health, which is looking into his claims.

He worked with a Canadian pharmaceutical company to create the blanket's coating, which is a closely-guarded secret.

The coating is such that the anti-bacterial agent retains its effectiveness despite the blanket being cleaned Gwyn Sullivan

"The beauty of the blanket is that once it is impregnated with the anti bacterial agent no bacteria can survive on it, unlike conventional blankets which can easily become contaminated," said Mr Sullivan.

"It also keeps bacteria off any sheets that are used in conjunction with it, and whereas you have to launder conventional blankets, these can simply be wiped clean without affecting their anti-bacterial properties.

"The coating is such that the anti-bacterial agent retains its effectiveness despite the blanket being cleaned."

Mr Sullivan hopes the blankets will become standard issue in the NHS, should his claims be proved, and is already setting up a manufacturing plant in Swansea.

A Kent company, Thermal Solutions International, will distribute the product.

His idea is also being checked out by health agencies in America, where vets already use it to stabilise the temperature of animals having operations, and to reduce the risk of infection.

The inventor - whose previous creations include wall ties for the building industry and specialist welding sets - has filed for a patent.

The blanket is also useful for allergy sufferers because bed mites cannot live on its anti-bacterial coating.