I just got a quick glimpse of these hoverflies mating, then they separated and flew off.
No interactions present.
Unfortunately, the angle of the photo precludes a definite ID. Do you have a photo from the side which you could add?
My Flickr photos...
They flew off as soon as I clicked the shutter.
My system is: First take a photo; then take a good photo. In case this happens.
That's exactly what I do, too. Record shot first and then edge forward for better pics. And if it is at all an unusual looking fly, then the photo is forgotten and the net comes out first!
Lat/Lng: 51.338268333333, 0.071143333333333
OS grid ref: TQ443619