Speedwells (Veronica spp.) are pretty, blue-flowered perennials that look attractive in a flower-rich lawn. However, their ability to root quickly, even from small sections, means they can quickly get out of hand in both lawns and borders. Germander speedwell (Veronica chamaedrys) is a stronger growing, coarser species than V. filiformis, flowering March to August. It is native in grassland, open woodland and hedgerows throughout the British Isles. It is usually troublesome in less frequently mown grass but can adapt to, and survive under, close mowing.
The flower is probably smaller than the nail on my little finger. But the macro lens makes it look a lot bigger. I spotted this in my garden on Sunday afternoon.