It specialises in manufacturing lightweight carbon composite components, such as engine casings.

It has been sitting on a fuel-saving box-wing concept for about 30 years — waiting until advancements in lightweight carbon composite materials made it viable.

The plane, the first to be made largely of lightweight carbon composites, has had a chequered history.

The clouds, which will cost 310,000 each, are made from a lightweight carbon structure and carry a giant envelope of material containing helium.

All it has, in fact, are two 40ft lightweight carbon fibre hulls, a long mast and three enormous sails.