From last spring: germander speedwell (Veronica chamaedrys). According to John Hutchinson (British Wild Flowers, Volume 2, Penguin Books, 1955),
The flowers of this plant are very beautiful when seen through a hand-lens. Nectar is secreted in a fleshy disk around the base of the ovary and protected by hairs partly across the mouth of the corolla. The two stamens are lateral and divergent and are seized by an insect alighting on the flower and drawn against its body, on which pollen is deposited and carried to the stigma of another flower.
The pollen at the ends of the stamens is visible in the above photo as the white blobs in front of the left and right petals.
Photo taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-05-03.