Black hoverfly with yellow markings (or possibly wasp?)

Black hoverfly with yellow markings (or possibly wasp?)

Observation - Black hoverfly with yellow markings (or possibly wasp?). Description: A black hoverfly (or possibly a wasp?) with yellow markings spotted while taking part in the 2012 Garden bioblitz. After watching it flying from plant to plant it eventually burrowed down into the soil in a flowerbed. Any help with ID most welcome.

A black hoverfly (or possibly a wasp?) with yellow markings spotted while taking part in the 2012 Garden bioblitz. After watching it flying from plant to plant it eventually burrowed down into the soil in a flowerbed. Any help with ID most welcome.