While I’ve seen these down by the river I have never seen on in the garden before.
Only two species of damselfly in Britain have obviously coloured wings. They both belong to the genus Calopteryx. In this species the wings of the mature male have a dark blue-black band across the central portion and those of the female are iridescent pale-green. The body colour is metallic blue-green in the male and green with a bronze tip in the female. The flight is fluttering, butterfly-like and the male often perform a fluttering display flight in front of females.
Mainly found along slow-flowing lowland streams and rivers, particularly those with muddy bottoms.