Common Hawker Dragonfly
This dragonfly has been identified for us as a "Common Hawker, a male. They can be quite variable in colour. This one has perhaps lost some of its lustre having been on the wing for a while."
The costa (leading edge vein) of a Common Hawker is yellow in both sexes; this can just be seen.
The Common Hawker male is supposed to have blue spotson the abdomen; Both sexes are supposed to have yellow ante-humerals and blue eyes. The ante-humerals are the top-most big white stripes in the photo.