You’ve got one of our 4 Emerald Damselflies [ unless you have only the 2nd ever record of a Winter Damselfly in the UK 🙂 ].
2 of the UK’s Emerald Damselflies are generally quite distinctive (but note the warning which follows) and these features are gender neutral:
Warning: There is some potential for confusion with regard to the Willow Emerald Damselfly thorn shape – Scarce Emerald Damselflies can also occasionally show a pronounced thorn BUT they do not also show a clear antehumeral stripe:
Neither of the above? The remaining 2 Emerald Damselflies require a bit more work.
Are we dealing with a female or a male?