This grower is sure of this plant identification.
this is the violet species
which has masses of starry,violet-blue flowers
Campanula lactiflora (Bellflower). This species is a very long-blooming perennial, it is ideal for a perennial border which will grow to a height of nearly 2m. It will produce pale green foliage and in the summer clusters of pinkish purple flowers will appear until the first frost.
It may need staking.
Border. Summer interest.