I saw this same aircraft, north of Shrivenham crossing east to west (the sound made me look up). In clear conditions the aircraft had a dark finish and looked more modern than others have suggested, but it wasn't a profile that I recognised.
Later on, a 3-ship trundled pass - Shorts Skyvan (in dark finish) , one of those Cessna twin-boom thingies, and a JP5; again just north of shrivenham crossing west to east.