A male Tephritis vespertina (Diptera: Tephritidae). Another first for me. The wing tips are mostly black. The larvae are known to feed on various dandelion-like plants such as cat's ear (Hypochaeris radicata), hawk's beard (Crepis sp), and bristly ox-tongue (Picris echiodes).
Photos taken in Whiteknights Park, Reading, UK, on 2012-07-05.