Unknown hoverfly yellow black triangular markings

Unknown hoverfly yellow black triangular markings

Observation - Unknown hoverfly yellow black triangular markings - UK and Ireland. Description: Unknown hoverfly spotted while taking part in the 2012 Garden bioblitz. Not a great picture I'm afraid but it didn't hang around for long. Any help with discerning the species would be most welcome.

Unknown hoverfly spotted while taking part in the 2012 Garden bioblitz. Not a great picture I'm afraid but it didn't hang around for long. Any help with discerning the species would be most welcome.