Not your usual hoverfly

This is not a normal hoverfly. Trust me. It's a whopper.  It looks like some kind of weird hybrid between a hoverfly and something that is bumblebee sized.  Bear in mind that it's sitting on a ragwort flower, not a dandelion.

Any ideas as to what this imposter could be?

Also, I'm thinking about investing in an infrared camera (ideally one that has already been converted)... any hints or tips or things to bear in mind would be very useful.