Two flies, probably of species Tephritis neesii (Diptera: Tephritidae), on the leaf of an ox-eye daisy (Leucanthemum vulgare). I have seen quite a few of these flies on my walk on Wednesday (May 2nd).
This is a closer view of one, showing the wing pattern more clearly:
And this is a mating pair:
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2012-04-30 (first photo) and 2012-05-02 (second and third).