Sorry about the poor quality of this photo. The subject never stopped moving and I was lucky to get a picture even as good as this. It is just about good enough to get an identification from, and Patrick Roper has confirmed this ID for me. This is the cranefly Ctenophora pectinicornis and it is a Nationally Scarce species. There are half dozen or so earlier records of this in Sussex, most of them before 1960. Associated with rot-holes in large broadleaved trees, especially beech; larvae often occur in the rotten shattered ends of trunks and have been found in rotten boughs which have freshly fallen from at least 10m up.