Looks like Impatiens glandulifera. Common name Himalayan balsam. http://en.wikipedia.org/wiki/Himalayan_Balsam This is now everywhere along rivers and along the lanes and verges in Britain. It is a real pest.
AKA Police man's Helmet, Poor Man's Orchid, Touch me not. When seed pods are ripe just touching them causes an explosion of seed all over the place and you'll have 2-3 times more next year. They do pull out easily though. Check out the "Botany Photo of the Day" on the far right of this screen opposite your post. Pics of another in this family. barb
