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The proposed Skylon vehicle would operate like an airliner, taking off and landing at a conventional runway.

Its major innovation is the Sabre engine, which can breathe air like a jet at lower speeds but switch to a rocket mode in the high atmosphere.

Reaction Engines Limited (REL) believes the test campaign will prove the readiness of Sabre's key elements.

This being so, the firm would then approach investors to raise the £250m needed to take the project into the final design phase.

"We intend to go to the Farnborough International Air Show in July with a clear message," explained REL managing director Alan Bond.