It's Volucella zonaria, the Banded Hoverfly. This and the other members of the genus Volucella lay their eggs in the nests of social wasps, the ensuing larvae feeding on the midden (dead wasps and detritus) that builds up in the nest, they probably help themselves to a few wasp larvae/pupae as well.
In the 1950s this species was relatively rare and confined to the extreme south east, it slowly expanded its range in favourable years and exploded in the last 15. It is now a common garden insect in the south, but despite its appearance has never been found associated with hornet nests, only those of the other social wasps.
Thanks to Anne Booth for the picture (click on it for a larger picture).