The tourist who posted it on the internet wrote: "First we thought it was a parachute but it was way too high up.

"It changed shape but stayed there for at least 30 minutes. Then I lost sight of it."

The sighting emerged shortly after a retired US Air Force major predicted extra-terrestrials would visit Earth to see Wills and Kate tie the knot.

UFO researcher George Filer said mystery craft were often spotted during major world events.

He claimed he had already been tipped off by RAF pilots about an increasing number of recent sightings over the English Channel.

A TOURIST filmed a UFO hovering over Westminster Abbey - the venue for tomorrow's Royal Wedding.

The 2½-minute video footage shows a shimmering white object in a cloudless blue sky near Big Ben.

It seems to move and shift shape - but to have three sections, like the starship USS Enterprise from TV's Star Trek.