Family Lestidae. These rest with wings at 45° to the body, unlike other Zygoptera.
This species is a recent arrival in the UK and has been establishing itself in Suffolk and parts of Norfolk and Essex since 2009.
The first confirmed records for Cambridgeshire seem to have been in 2014.
Unlike the established Emerald (Lestes sponsa) and Scarce Emerald (L. dryas), mature males lack blue frosting, and have pale pterostigmata.
The inferior anal appendages (second photo) are much shorter than in the Lestes spp.