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I bought the house a couple of months ago, Chipchopper, and on the forms the previous owner had filled in, she’d ticked the “no” box for “is there any Japanese knotweed.”
I can only describe it as looking like pampas grass but without the feathery bits. There were frond-like things growing from it.
Because it’s all in one section, I’m guessing that it was planted deliberately, and not some sort of invasion.
Off out now, but thanks again for all the answers.