Strange fly?

I'd love to know what kind of fly this is? At first when it was buzzing around, I thought it was a bee but seeing it close up and those eyes I suspect it's more of a fly. I did get a shock when I saw the face of a cow on it!
Anyway, Rob and I had a long car journey today (bloomin' M25) but luckily we were listening to an incredibly exciting audio book "14" by Peter Clines, read by the wonderful Ray Parker. One for all you sci fi fans out there.