Driven by the need to reduce fuel costs and defuse political pressure, the aviation industry is pouring millions of pounds into developing greener planes.

The most striking prototype is the "blended wing" jet, where the plane is built as a giant wing and burns a quarter less fuel than a conventional aircraft. It also has improved aerodynamics. The blended wing is in development by various organizations, including Boeing, which flew a 7 m prototype last year. However, Boeing has ruled out a passenger version until 2030.

Rolls-Royce is testing a prototype based on fuel-cell technology which combines hydrogen and oxygen to produce electricity. However, it is impractical for passenger aircraft because a fuel cell takes up to 50 times more space than a conventional engine.