First pics I look at and I find a slight anomaly probably a bug, wasn't a plane....and remeber this is Silbury hill
its as big a UFO hotspot anywhere on the planet...
odds are bird or unknown ................
http://www.flickr.com/photos/sengoksa/7663705982/in/photostream
This is an almost identical image to mine taken in august of 2009... Colin Andrews sent it to Bruce mcabee
for analysis.....
http://www.colinandrews.net/UFO-PoliceSergeant-Silbury2.html