Little green men are strictly confined to pelican crossings, according to a Bradford University boffin who has exploded the theory of life on other planets.

Professor Peter Excell reckons the chances of intelligent alien life - green or otherwise - are as distant as one in a hundred billion, far more remote than currently believed.

"It is quite possible that the Earth is unique," said Prof Excell. "The Earth-Sun system is so intricate it would be highly unlikely that it has been matched anywhere else."

The crux of Prof Excell's argument lies in the finely balanced eco-system that exists here on Earth.

"We rely on the sun for heat and light, but it also throws out a lot of harmful effects, such as ultra-violet radiation which would kill us if we were not protected by the atmosphere," he said.

"The harmful stuff is absorbed and the ionosphere created as a by-product, while the Earth's magnetic field also sweeps harmful particles away.

"The whole system is extremely delicate and my suspicion is that you only get intelligent life in a system which is as finely balanced."

Believers in alien life say there are about one hundred billion stars and each will have at least one planet in orbit, meaning that life must exist out there somewhere.

But Prof Excell said: "My view is that this is far too cavalier and that the probability of the order of one in a hundred billion, or even smaller is entirely possible."

Prof Excell is based at Bradford University's department of Electron-ics and Electrical Engineering and is a world expert on the work of Bradford born Nobel prize winner Sir Edward Appleton, who proved the existence of the ionosphere.

And he is responsible for the great scientist's inclusion in a £4.7 million exhibition centre planned by Bradford Cathedral, called the National Millennium Faith Experience.

However, one of the region's leading ET experts disagreed with the Professor's hypothesis.

"The existence of extra-terrestrial life is still to be proven, but it has not yet been disproved," said Russell Kellett, Bradford based founding member of the International UFO Research Network.

He said countless sightings of UFO's, some 30 in England this year, meant there had to be some form of intelligent alien life in the universe: "Let's put it like this, if there are no aliens, then someone is messing us around."

A spokesman for the Royal Astronomical Society said there was no real academic consensus about intelligent life on other planets.

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