It was imported into the UK by a German doctor. He had been in Japan and brought back species of plants that he found to be quite exotic. In the late 19th century a trend in the UK called wild gardening tried to position the ideal garden as something that wasn't meticulously curated. knotweed was a perfect plant for that. And so what's the scale of its spread now? It's difficult to quantify because there's been no major survey done of knotweed in the UK. You can spot it in the Auckland Islands, in the Shetland Islands all across Scotland but predominantly you will find it in major cities.