This pretty little plant, a familiar sight on old walls, goes by the name of ivy leaved toadflax (among many others). Said to have been introduced to Britain accidentally along with ornamental sculpture from Italy, it grows abundantly on masonry in great hanging clumps speckled with tiny mauve and yellow snapdragon-like flowers.
Its profusion is due to an unusual adaptation: it plants its own seeds. When in bloom the flowers face towards the sun, waiting to be pollinated by bees but once fertilized the seedpods are swiftly directed in the opposite direction, away from the light, their tendrils seeking dark cracks and crevices that will provide a shady environment for the seeds to germinate.
This is called skototropism, the reverse of the phototropism demonstrated by the beans I blipped in April (which I'm pleased to say are doing well.)