Rosebay Willowherb (Epilobium angustifolium) is in flower wherever it can take hold: field margins, waste ground, railway embankments and disturbed ground generally. Prolific is the word that springs to mind. I noted recently that the white flowered form in the garden is attracting bumblebees [entry dated 11th. July] but this patch was buzzing with honeybees. The white form is sometimes cultivated as a garden plant by wild gardeners like me but in the wild I have only seen E. angustifolium with the vivid magenta/pink inflorescence. 
 In its native habitat of North America the plant is known as Fireweed- not a reference to these fiery hues. It flourishes after areas have been scorched by fire; my father tells me he saw it growing on bombsites all over the East End. Perhaps those conflagrations are one of the reasons it came to be such an abundant weed/wildflower here in the UK. 

 NB Strictly speaking I must correct myself by noting that E. angustifolium has been reclassified as Chamaenerion angustifolium though both names seem to be in usage.