In a vast Farnborough hangar, the wings of the largest aircraft made in Britain recede into the far distance. Despite its size – at 85 feet, the wingspan is considerably greater than an executive Learjet – I could probably pick it up if I was allowed to. The Zephyr, made by Aalto, weighs just 65kg. Its light weight helps the craft reach dizzying heights. Unlike conventional aircraft, which typically fly between 30,000 and 40,000 feet, Aalto is one of several British ventures blazing a trail in the stratosphere, the region of our airspace that starts at 60,000 feet. “It flies at twice the height of airliner, but at the speed of a bicycle,” staff politely explain on the production line. It’s here, in the cold, thin air that was previously the sole domain of spy planes like Lockheed’s U-2, where Britain has taken an unlikely pioneering lead. Aircraft that inhabit this domain are called “High Altitude Platforms”, or HAPS. “It’s a pseudo satellite,” explains Tim Robinson of the Royal Aeronautical Society. Not quite in space but above the weather systems, these HAPS can offer the same services as a satellite: chiefly, imaging and communications. Aalto – a loss-making business that...