Flower head looks similar but it's yellow rather than pink. Also It stood only about a foot high on the edge of a river
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it isn't native. It was apparently introduced to Britain from the Aleutian Islands (off Alaska) in the early 19th century. It is well established in several areas, but doesn't seem quite as aggressive as the awful Impatiens.
Lat/Lng: 53.2161, -1.6746
OS grid ref: SK218688