LONDON (Reuters) - A team of scientists said on Wednesday they had made a major leap toward developing secure global communications.

Researchers from QinetiQ, the commercial arm of Britain's defense research agency, and their colleagues at Ludwig-Maximilian University in Munich have sent a key for deciphering coded information over a record 14.5 miles of open space between two mountains in Germany.

Keys are random strings of numbers needed to encode and decode sensitive data. The distribution of keys is essential for secure global communications.

"This is the only way to distribute keys for encoding data in absolute security without actually sending a guy with a briefcase," John G. Rarity, of QinetiQ, told Reuters.

In a global system the keys would be sent to a satellite which would act like a relay station for distributing them around the world.

The keys, which use quantum cryptography, were transmitted as photons of light along optical fibres. If a key has been intercepted and read it changes the state of the photon so the recipient knows that it has been intercepted.

If keys are sent electronically they could be intercepted and no one would know it.

"It is quite a technical challenge to point a beam of this sort of low-intensity light over long distances. The great technical challenge is to try to do it between moving things like a satellite," Rarity, whose research is reported in the science journal Nature, added.

The initial users of secure global communications would be governments.

"Government secrets will want to be kept for a long time so you would want to make that security uncrackable by a computer running day and night for many years," Rarity said.

But he added that in the longer term, when it is more user friendly and cheap, it could compete with other systems.