The Migrant hawker (Aeshna mixta) is extremely common nowadays. Hard to believe that it was once known as the Scarce Hawker! Although it breeds natively, numbers of this autumn dragonfly are boosted by migration from the continent. In good years (i.e. 2004) considerable numbers arrive and can be found hawking the streets of Norwich like miniature House Martins.
Can be confused with Common and immature Southern Hawkers, but the faint or missing ante-humeral stripes, the exceptionally long anal appendages and the distinctive down-curved tail in flight should distinguish it. In flight the blue "saddle" on the underside of the abdomen, just behind the thorax is quite distinctive in males.