This isn't really a quiz question, but as Rolf Harris might say- can you see what it is yet?
Emperor Dragonfly (Anax imperator)
One of the reason for visiting the lake at Bushy Ruff was to see if the Emperor Dragonflies were around yet, and I wasn't disappointed. There were at least three around and at one time I witnessed them in a group chase around.
The slight downward curve of the abdomen is immediately obvious and a good first clue to the identification. Mature males are blue with a black dorsal line. It is one of the largest of our dragonflies, and it is a voracious hunter, continually chasing and catching small insects over the water.
Although this picture isn't as sharp as I would like, it does show the strange angles and twists that the wings take during flight.