Hairy bittercress (Cardamine hirsuta) (see image above) is an annual species, common throughout the British Isles, particularly on bare ground, path-sides, and on walls. It may often be seen growing on the surface of containers in nurseries and garden centres and the seeds can be introduced into gardens unwittingly with container-grown plants.
Remove young plants before they get a chance to flower and set seed. Pull them out individually by hand or hoe off young seedlings and remove from the soil surface. Avoid deep cultivation which brings up new seeds. Apply a mulch to the surface after weeding to prevent further germination.