the speed for this distance

This is all i can tell you, i am a 64 year old male living in the uk, And i was not intoxicated, and on no medication at that time.
It was a very clear and bright afternoon, no clouds, i was in my Garden for my dog to do her toilet, when i looked up into the sky, Not looking at anything specifically, when i saw something moving At incredible speed? This was not a plane, and not a satellite, planes don't fly  this high It was too high to distinguish the shape, but the colour was lead like, dull Grey?, This ufo was way higher than 10,000 feet, although it was tiny to look at, (nothing earthly goes at that speed, at that distance away)??