I was driving home from work on a summer evening in june 2017, in daylight, half 6, on a cloudy, blustery evening. on a country lane, 15 miles south of oxford, i saw a car stopped by the side of the road and the driver out of the car holding an ipad up photographing the sky low down to the north east. i looked over and saw a huge metallic disc; a classic ufo shape, was visible in a gap in the total cloud cover. i slowed the car but didn't brake hard as i had a speed merchant on my bumper. i observed the disc for approx 15 to 20 seconds until a line of trees obscured my view. the disc was approx 20% obscured by cloud which made it easier to estimate its distance and size. this disc was approx 500 metres in diameter - half a kilometre! it was at least this large! it was shiny, metallic and with a raised edge. the edge was alternate silver and black panels. apart from its size, the most surprising fact was it being so stationary; as the clouds rolled on it was completely static. it was also tilted over at around 15 degrees. it was not a balloon or airship, and anyway the weather wasn't suitable for such things. i drove on till i'd passed the trees and stopped around a corner about 400 m further on to get a better view and get the car behind past me. the cloud cover had closed up. i waited and saw no more then it started to rain. oddly i didn't return to see the person with the ipad. i assumed it would be all over the local news the next day. i am a 58 year old engineer that estimates sizes and distances for a living, i know what i saw was not anything normal - and it was massive. i went home, my wife and family found it all very amusing. everyone i know has heard my tale, they laugh too and no-one believes me. why are so many people so short-sighted and unable to believe? the person with the ipad remains a mystery, i scanned the local papers and internet for anything, but nothing! i haven't stopped kicking myself since for not going back to see ipad man and get his pictures. days later i happened to drive under the location about 2 miles to the north, where i estimated the ufo to be and wondered what there was to see. there i saw a large solar farm (i'd forgotten about it as it's not so visible form the road). i believe the ufo was hovering over this and looking down on it. why else would it be tilted over? the size, the solid metallic shape and it's edge features were all real. it's odd tilt, partly obscured by cloud and its completely stationary position on such a stormy evening all contributed to it being the firm ufo sighting of my lifetime. i have not stopped berating myself since for not returning to the other witness for his photographic proof. why didn't he go public with his photos?