Small purple flower to ID

This little purple flower has just come up in my spoil heap. It doesn't look like anything I've bought and accidentally dropped, I don't think, and yet it sort of looks bulb-like in the way it's growing, so I don't see how it could be a self seeded wildflower, really. Does anyone have any ideas? I realise it may be a lot easier to identify once the flower has finished opening up, so I will try to take one later if I remember. Thanks!