Recently uncovered plans show bosses filed for a patent in 1970 for a spacecraft powered by "controlled thermonuclear fusion reaction".

With a passenger compartment upstairs, it would have been cheap to run and super-fast, according to its inventor.

The proposals were recently found on the European Patent Office website.

The original patent application said the reaction would be "ignited by one or more pulsed laser beams".

The application was made on behalf of the British Railways Board and the patent was granted in March 1973.

A patent document reads: "The present invention relates to a space vehicle. More particularly it relates to a power supply for a space vehicle which offers a source of sustained thrust for the loss of a very small mass of fuel.

"Thus it would enable very high velocities to be attained in a space vehicle and in fact the prolonged acceleration of the vehicle may in some circumstances be used to simulate gravity."

But, it seems, the patent later lapsed because of non-payment of renewal fees, while the spaceship - the invention of Charles Osmond Frederick - clearly never materialised.