Spanish Bluebells, Hyacinthoides hispanica. It will take over a large area without any help from you. My 'thinning out' consists of digging them up and throwing them away. But they serve a purpose in an informal garden with plenty of space in regions where they cannot interfere with the gene pool of native Hyacinthoides non-scripta. Bluebells as weeds

My 'thinning out' also consists of digging them out and throwing them away...every single year. I have, just this week, spotted a pink interloper underneath a particularly vicious rose (Pleine de Grace) which will have to be removed (sigh). Where do they come from? How do they get here? I absolutely know I am not planting the buggers.