Baccha elongata is a small hoverfly with a slender wasp-waisted shape. It is the only British hoverfly with this distinctive appearance (although a couple of others, having swollen thighs, might be mistaken for it).
Colloquially called the Gossamer Hoverfly for its delicate shape, this insect likes dappled woodland and hedgerows. It frequents the lower regions of denser vegetation, where it can usually avoid attention - which explains why it is difficult to photograph. Its larvae are predators of ground-layer aphids.
The individual photographed here has its right wing temporarily folded under its body.