I don't think I have seen one of these little beauty's before. He is a species of Robber Fly, ( Laphria flava) and in the British Isles is only found in Northern Scotland.
Robber Flies are predatory flies and are perfectly equipped to this life style.
They sit on a branch and wait for another insect to fly past, then they dart out and catch the insect using their bristly legs to grip them tight. Robber Flies have a very sturdy proboscis which they use to puncture their prey and literally suck them dry.
To prevent their prey damaging their eyes, Robbers have a bristly mound or beard on the face to keep the prey well away.
