Paul,
It won't be a Hairy Dragonfly, they are the earliest to emerge (May) and their flight season is now well and truly over. Given it's blue and green colour and the very broad antehumeral stripes (the big green marks behind the head, the shoulder blades if you like), the fact that it was in a lane and presumably came close to you, given that you were using the 20mm lens I will go for Southern Hawker (they can be quite curious and come up to investigate you).
Barrie