UK to Australia in just four hours
Hypersonic passenger jets of the future could whisk Aussies to the London in just four hours, experts say.
The journey usually takes around 19 to 20 hours - but flight times could be slashed by a new jet engine currently in development.
British firm Reaction Engines is working on a new engine that can propel an aircraft to Mach 5.5.
That's more than five times the speed of sound, resulting in a top speed of around 6437kph.
The SABRE (Synergetic Air Breathing Rocket Engine) says the engines could be operational as early as the 2030s.
"This is not sci-fi. This is not a pipe dream. This is literally in the works," said Dr Graham Turnock, of the UK Space Agency.
"It has the potential to turn air travel on its head.
"Certainly the way you conceive air travel will completely change in ten years' time."
The engine solves a major problem of high-speed air travel: melting.
Typically such fast propulsion would require huge temperatures that would cause the engine parts to melt.
But SABRE uses liquid gases - including helium - which can cool incoming air from 1000C to -150C in one-hundredth of a second.
And it does this without creating any ice blockages.
SABRE will also be powered by hydrogen - an eco-friendly fuel that produces water vapour when it burns.
The goal is to create a space-plane called Skylon that could take off from a spaceport - like the one set to open in Cornwall in 2021.
It would soar in to the sky and then fly in a low Earth orbit before re-entering the atmosphere and landing back on a runway.
"It would not only allow you to fly around the world hypersonically, and take people from London to Australia outside the atmosphere and have far less long term effect on the atmosphere but it will also allow you to rapidly get much more technology into space," said Will Whitehorn, of trade body UK Space.
It's possible that the space-plane could achieve ludicrously fast speeds of 19,000mph (Mach 25) while travelling through space.
Space-planes have several advantages, making use of a speed boost from the Earth's rotation and orbital pull - as well as less resistance to motion.
Unmanned test flights for early prototypes of a SABRE-powered space-plane are tipped to begin as early as 2025.
But commercial flights may still be decades away.
Oxfordshire-based Reaction Engines has received around $A109million from the government.
Flight tech firms Boeing, Rolls-Royce and BAE Systems have also matched the figure.
How much would you be willing to pay for a four hour flight to the UK? Let us know in the comments!