Unknown Flower

The weather was much improved today with temperatures in the high teens (centigrade) so I took the opportunity to do some more tidying and weeding. My garden is a rather random affair as I let things seed themselves and spread around. If I like them where they are they stay and if I think they are in the wrong place I pull them up.

I bought this plant with these hanging purple flowers last year but I have no idea what it is. It dies down during the winter but it seeds easily and has come up again in almost the same place. It's definitely a keeper. If anybody knows what it is then do let me know.