I was walking back through in the woods between the car park of the Napier Road Tesco's and the mouth of the River Kennet, laden with bags of shopping when I saw a metallic-green eyed fly on a flower. I immediately thought 'horsefly' and put my bags down to get a closer look. It held its wings partly open and in the middle of each wing was a largish dark patch. The thorax and abdomen were brownish and black, with longitudinal stripes on the thorax. There was a suggestion of a yellowish patch on either side of the front end of the abdomen. Unfortunately I did not have my camera with me. I tried to catch it in a plastic sandwich box but the fly escaped and flew off.
On getting home I had a look through Stubbs and Drake and was able to identify it as a female Chrysops sp, possibly Chrysops caecutiens (Diptera: Tabanidae). Members of this genus sometimes known as deerflies; I have twice seen muntjac deer (Muntiacus reevesi) on the railway embankment near Tesco's.