Red Valerian

 Centranthus ruber. Hardy perennial that grows prolifically in hot, sunny dry walls and banks, but doesn't like a border situation. Red starry flowers top 2-foot stiff glaucous stems throughout late summer and autumn, attracting Hummingbird Hawkmoths and Silver-Y moths that fly over from the continent in hot summers. Also liked by butterflies, hoverflies and all the beneficial insects.