Although he doesn't believe in little green men, Mr McFadden, who is also a rocket scientist, is adamant that UFO's do exist but may be entirely man-made.

"It's not unusual to see UFOs, there are certainly plenty of things up there that cannot easily be identified by the average person, or even by scientists or commercial pilots, and I am both.

"I remain a firm non-believer in UFO's from Outer Space, but I have seen things that I believe are more like secret projects than little green men," he said yesterday.

With decades of experience in this particular field, Mr McFadden knows about space more than most.

"I've definitely seen things I can't identify, one was in retrograde orbit in the early 60s and was moving in the opposite direction of the Echo 1 satellite, which moves in the direction of earth's orbit," he revealed.

"This thing was going west and the only logical way it could be going in that direction is if it came from somewhere else.

"The second time I saw something was when I was watching a B47 and a KC97 refuelling in mid-air, again in the early 60s.

Twice as fast

"They were at 30,000 feet, high enough to still be in the sunshine even though the sun had set, and something appeared far above these aircraft, going twice as fast. Nothing we owned back then could possibly have done that."

Having watched the skies for most of his life, Mr McFadden says it would be scientifically impossible for life outside our solar system to travel to earth," he added.

"If there are UFOs, then I believe they are something on earth we don't know about, either from America, or Russia or China maybe. I believe this simply because the distances involved are so vast. At the speed of light it would take us four years to get to the nearest star, so you would be looking at a trip of thousands of years to even reach some far-off conceivably inhabited star."

"There are certainly things out there flying around that we don't know about, but that's only because they don't want us to know about them," he added.