Which blue damselfly?
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The black "U" shaped mark on abdominal segment 2 on the blue male, together with the uninterrupted antehumeral stripe on top of the thorax helps identify this damselfly.
The only real confusion species would be the Variable Damselfly but the male has a transected antehumeral stripe that looks like an exclamation mark.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
Lat/Lng: 51.293, -0.3846
OS grid ref: TQ127561