Anyone who has grown onions in their garden will probably recognise this flower immediately, the wispy little florets growing from what appears to be a cluster of seeds; once pollinated they do, indeed, become seeds of course. All the onion (or allium) family have flowers like this and the wild onion (Allium vineale) is no exception. After ramsons, the wild garlic, the wild onion is the most likely member of the family to be encountered in the countryside. It grows in bare or sparsely grassed places and can be a real problem in agricultural settings if it gets established as it can give cereal crops around it the taste and smell of garlic; ready made garlic bread perhaps?
This is also commonly known as crow garlic, indeed two of my reference books call it that, the other three settle on wild onion. Wikipedia uses wild onions to reference all members of the family that grow wild and uses crow garlic for this particular species. Whilst edible it is not considered suitable for human consumption like cultivated garlic as it is much stronger in flavour and does tend to spread its aroma about!