Hoverfly? No!

There are apparently over 270 species of hoverfly in the UK, so it's not surprising I could not definitively identify this unusual one sharing its feast of nectar from water mint in my garden pond with a bluebottle fly. I considered bees, wasps or hornets, but they have antenna and the eyes are wrong, so hoverfly it is unless someone knows better.

Now identified as a Thick-headed fly!