Please can someone identify this plant for me. It has just started growing in my garden. I didn't plant it but I think it may have grown from seed from the birdfeeder. It is about 50 cm high and the flower grows from the point where the leaf joins the stem. The flower has a very unusual base and the plant exudes a milky sap when cut.
your mystery flower is a Campanula. Of the native and regularly grown species several +/- fit the bill. The flower has a pedicel (flower stalk) so we can rule out Campanula glomerata - the clustered bellflower . It looks to me probably to be Campanula trachelium - the Nettle leaved Bellflower. I wouldn't expect its seeds to be in bird food but it is probably sown in some wild flower mixes, or might be lurking as a native nearby?
I've just looked that up and it looks very much like it. It has now grown to about 2 m high, and the leaves feel slightly prickly. I'm still wondering how it got into my garden - had a peek at the neighbours, but haven't seen anything similar. However, it is a beautiful flower and I'll make sure I collect some seeds when the flowers are finished.