Bug-Eyed

This is NOT a hoverfly. In fact it EATS hoverflies, or at least, its larvae do.

You can tell it isn't a hoverfly because:
a) It has long antennae.
b) Its eyes, although large for a wasp, are smaller than a hoverfly's and don't come anywhere near to meeting on top of its head. In fact, there are three secondary simple-eyes called ocelli that are visible on the top of its head.
c) It has two pairs of wings though those are not visible here when the wings are folded back.
d) It has a narrow waist between the thorax and abdomen.
e) Jaws. No hoverfly ever has jaws like these.

It is in fact a type of solitary wasp sometimes called a 'digger wasp'. This one belongs to the genus Ectemnius. There are at least 10 species from this genus that are found in the UK and some can only be told apart by microscopic examination of a specimen.
I have checked the BWARS website (http://www.bwars.com/index.php?q=species_gallery/Ectemnius) and none of the images exactly match but the images of the same species sometimes show variation, making it harder to ID just from the image.

Those jaws are used to excavate a deep hole, either in rotten wood, or in the ground. This is stocked with the bodies of several flies that its larvae will feed on.

This solitary wasp is similar to a slightly smaller related species that I blipped almost a year ago (http://www.blipfoto.com/entry/3382923) - you may remember it?

Spotted in my Fife garden.