I picked a single stem and hung it over the gorse: prefeeable to kneeling down in mud and dog fewmets!
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I think that the flower colour is consistent with cicuta58's suggestion. This is by all accounts now well-established, but I've never before seen a "definite" example. There are a few other garden escapes in the surrounding woodland.
I've changed the title accordingly.
Lat/Lng: 54.5712, -1.0263
OS grid ref: NZ630199