I wonder if anyone can help with identifying a weed that my Dad has in his allotment (in fact many of the allotments in that area do)? It grows about 15 inches tall, and has white flowers. The flowers almost look like they could be a grass 'head' and they are definitely what will fly off and set seed elsewhere. I did have a bit but it wilted between there and home in the heat!
Any ideas on what it is would be gratefully appreciated (and any magical ways of preventing it coming back! We don't use chemicals.)