Hoverflies come in all sorts of guises, some mimic wasps, some bees, some quite slim, even very small, and others much bigger and chunkier. One thing that instantly distinguishes them, of course, is their incredible ability to hover and to fly at exceptional speeds - nought to gone in less than a second!
You often do not get much to go on when identifying them, the designs on their body being the usual feature but unless they are perched on a leaf or taking nectar from a flower they can be difficult to get a close view of. To actually distinguish between some species you need a microscopic examination!
With this one, I disturbed it from a bramble bush alongside the river Piddle on Wareham Common and as I did so it revealed a bright reddish orange thorax which may be just discernible from the photograph. To complete the identification I needed my text book on hoverflies that says this species, Platycheirus granditarsus, is common on marshy meadows with lush vegetation and ditches and if one description describes Wareham Common it is precisely that!
So, no arguments, this is the awkwardly named Platycheirus granditarsus!