Sitting in my garden talking to my wife I saw fast moving object moving in a straight line across the sky. It caught my attention due to its speed of flight. It was too small for a plane and too fast for a bird. As I looked I could make out no discernible protuberances such as wings or fins - it was simply a small silver ball moving in a very straight line. It eventually disappeared from my line of sight as it flew over neighbouring houses moving roughly South. We have planes flying over head fairly regularly and in the next half an hour I observed two. The first a high flying jet which moved across the sky extremely slowly compared to the object I had seen. The second was a single engine propellor plane which appeared to be flying at a similar height but was noticeably bigger and quite clearly an aircraft.