A British company has designed an eco-friendly airliner that could make a trip from London to Sydney in under five hours.

Reaction Engines in Oxfordshire has received funding from the European Space Agency to design the plane as part of the Long-Term Advanced Propulsion Concepts and Technologies project.

The A2 airliner would be capable of carrying 300 passengers at speeds of up to Mach 5, or 3,800mph.

"Unlike Concorde the A2 has exceptional range (approx 20,000km both subsonic and supersonic) and is able to service a large number of routes while avoiding supersonic over-flight of populated areas," said Reaction Engines.

"This good subsonic performance enables it to service conventional subsonic overland routes thereby increasing its sales potential to airlines."

The aircraft, which would be twice the size of existing airliners, would fly at subsonic speeds out into the Atlantic before boosting into low Earth orbit and flying over the North Pole and down the Pacific to Australia.

It would run on liquid hydrogen, which contains far more potential power than hydrocarbons, and be capable of sustained high speeds.

Reaction Engines said that it has solved current problems with hypersonic travel, primarily airframe heating due to friction, and that a test flight could take place within the next 25 years.