Sisyrinchium striatum, I seem to remember that it will probably seed itself around as well.
Yes, I agree - Bit I don't find they seed - Just die back and return next year. After 2yrs I split them like irises and pop some in other places - Seem to like all conditions and nice and neat.
Did wonder about seeding biofreak but it has turned up in my garden and I didn't plant it?
mine seed around like mad. Always plenty of babies