The sighting took place on Wednesday 20th July 2016 above the M1 motorway North of London UK, on a straight section of road ( From 510 58 54.27 North to 510 59 26.97 West ) at 15:20 BST ( 14:20 GMT ) approximately. Weather conditions were bright sunshine with a few scattered cumulus clouds.I was returning home after a days work travelling North as I do every weekday. After passing through junction 12 on the M1 I continued on in light traffic. When the road curved around to the section I mention above I noticed what I thought was a light aircraft, although I could not make out any details it just seemed to be a white dot against the blue sky to left of the motorway high above and to the north of the trees. I was struck by the speed of the object that made me think it must be a high performance aircraft, which further tweaked my interest as I am a pilot and professional engineer in the aerospace industry.I was startled when it pitched down into a dive at 45 degrees. My first reaction was that it was going to do some aerobatic manoeuvres and felt I wanted to see this and find out what type of aircraft it was. As I watched it descend I was looking for wings and a tail but could see none. It descended to just above the motorway and then appeared to be flying just above the motorway traffic approaching in my direction. As it approached I realised it was circular and thought it must be a helicopter but could not see any rotors or other structures. When it passed the electricity pylon nearest to me on the right hand side of the road I could see it was a shiny silvery white sphere about 2 metres or 7 feet in diameter. It also had a yellow circular light at its centre. It then seemed to veer off towards the right hand side of the road descending and the last time I saw it it went behind the trees about 150 to 200 metres ahead on the right. I attach some slides I have made using images from Google Earth and Street View to show the location, path lengths and my position on the motorway. The last slide I constructed to show what the object looked like. The duration of the sighting was about fifteen seconds. The wind direction was from the south west, in other words at right angles to the motorway and the path the object followed. I said to myself afterwards What was that? I was shocked.