These lovely little insects are on the wing again, they are amazing with that incredibly long tongue used for feeding. This one is the very common Dark-edged Bee-fly, so named for obvious reasons.
Their larvae are parasitoids of the larvae of mining bees which usually nest in colonies in soil such as woodlands or even your flower beds and lawns. Female bee-flies hover a few inches above mining bee nesting areas and flick eggs onto the ground with a rapid twist of the body. They actually collect fine dust in a little chamber at their rear end just prior to this, as the eggs need to be dust-coated before they are laid.
The North Kent Marshes are a very special area and worth preserving at all cost.