Its got large green seratted leaves, white cone shaped flowers and produces large spiky ball shape things in the axis of the plant as shown in the picture. I presume its come from my wild bird seed that I put out? Im in the UK.
That is Datura stramomium, the thorn apple. But don't be tempted to take a bite because it's one of the nightshade family and is poisonous. I don't know if it came from your bird seed, it's actually a UK resident although not often seen. At least I've never seen one out of cultivation.