This is a "weed", grows in profusion in Guernsey. Often found in walls and between pavings etc. but this clump is growing quite happily in our driveway. Apparently it is much loved by Red Admiral butterflies and won't be weeded out by me.
Do the butterflies come for the flowers, or lay eggs on it? I think of it as "Llandudno weed", because it grows everywhere here, and I'd never seen it until I moved here. Not sure I'm willing to tolerate it - there are plenty of other plants in my garden for butterflies to feed on.