The pilot was blissfully unaware as he put the aircraft through its paces as part of a Battle of Britain memorial fly-past in Withernsea, Yorkshire.
However, the presence of a hovering black flying saucer soon came to light.
A photograph was snapped by a resident who only saw the mystery craft when he downloaded the image from his digital camera.
He said: ''I live in Withernsea on the east coast of England.
''On Saturday 15 June 2002, we were treated to a flyby by one of the RAF's Lancaster bombers.
''I took several snaps with my digital camera and, after downloading them on my computer, noticed one image contained an unidentified object (upper right and trailing the Lancaster) and looking decidedly triangular in shape.
''Nothing was noticed with the naked eye at the time.''
The photographer asked officials for more information.
But the Ministry of Defence desk officer who responded said there were no other reports of UFO sightings that day.
It was not possible to say whether there were military choppers in the area that day without contacting every squadron, the official said.
But he explained it might have been a commercial helicopter from an off-shore oil or gas installation
