This is Campanula repunculoides. I spotted it a few years ago at a church fete - garden stalls at church fetes are always manned by little ole ladies: I said to the LOL, 'I didn't think campanulas would grow up here this far north!' She said, 'this one will grow anywhere, and you can also use the tuber as a vegetable'. So I bought it ($1), stuck it in the ground and forgot about it. The other day, weeding around, I spotted this flower, 'well, bugger me!' I said to meself, 'what a gorgeous thing!' And so moved it to a more (in my opinion) favourable position.
B.
PS Excuse the 'light' I took the pic with the 'flash' on.