I was taking a cigarette break and was looking up at the sky, beautiful summers day Hampstead, London and saw a matt metallic orb moving with purpose of action at incredible speed travelling miles in a split second, stopping abruptly and hovering in place before taking off again in a zig zag fashion even though it was a mile (max distance) or so away it was clearly spinning and you could see that by the distortion of air surrounding it almost like convection currents you would see rising from a hot road blurring the visuals also looked like something was dripping off it like molten metal. There was no sound whatsoever i.e. like a plan when it moves this was silent I would say the speed would be close to 5,000 miles an hour, instant acceleration accompanied by instant deceleration. This size of the object most have been huge due to distance and scale had to be easily larger than a double decker bus. I was working for an automotive magazine as their art director and called my chief editor (petrol head) to take a look we both know about vehicles and speed etc. neither of us knew what it was, he proposed it was a weather balloon we both knew that was ridicules no weather balloon could move, change direction and jump from one end of the horizon to the other multiple times it is just not possible and we never talked about it again or at least he diffidently didn���t want to talk about the incident to anyone and I followed his lead everyone knows that people would just think your mad, the said incident took place in the summer of 1999 during my working week. At no point did a feel threatened by the object it seemed to be observing London was it alien, my feeling was it was very advanced tech, who was flying the vehicle that is a grey area indeed, I never lost sight of the object I returned to my work and it was still flying about when I finished observing it. I could have told others at the company to take a look but was concerned that someone would report it and we would all look like idiots for saying we saw a UFO and I was the first to see it.