A pretty weed?

To me Scarlet Pimpernel is a very pretty wild flower however, it has widely been classed as a pesky weed due to its success in growing on the poorest of soils. Here in North Pembrokeshire is one such Scarlet Pimpernel stronghold.
It is a very small flower, less than two inches high with a flower, such as the image above.
This image is from last June, shot in my rockery, very stony and poor soil.