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Not sure. I'm sure someone will know. Welcome to GOY. It is a very helpful site.

That looks like Impatiens (Policeman's Helmet) It is an imported and very invasive weed. The seed heads pop and scatter the seeds all over the place. It is killing off native plants along many watercourses.

Yes that's it . It is an annual, so next Spring watch for the seedlings which come up at a certain soil temprature. . I found if you kill them when they first show true leaves. No more will come up till the following spring, if at all. I am sorry to have lost mine as I enjoyed seeing them explode. another name is Noli me tangere (Touch me not)

Thank you very much for the welcome, and the answer to my question. I rather like this weed, and the bees seem to like it, so i will keep it under strick control, and do a lot of dead heading and pulling up those that i don't want. thanks again.

Oh dear...Owdboggy is spot on. This is also called Himalayan Balsam and is one of the top most invasive weeds. It is actually illegal to propagate it, take it to the tip, all sorts! It does spread rapidly and enjoys growing by water, especially moving water, so it gets along stream and river banks very quickly indeed. I do agree with you, it's much prettier that Japanese Knotweed, but it ranks with that pernicious weed on the 'Naughties' list!

You may look after it in your garden, but there are a lot of areas round even the most built up places where this appalling plant can grow and then it crowds out the native flora. It might not take over your garden ,but it pretty soon will take over everyone elses.