prob not a garden escape.
No interactions present.
The leaf-shape does not match native Aconitum napellus.
I think probably it is correctly named, rather than being the more common (as a garden escape) hybrid with A. variegatum, but it looks like it is one of the continental subspecies or at least has some foreign genes.
Difficult to deal with young plants!
Lat/Lng: 51.74082, -2.21352
OS grid ref: SO853047
shady spot, riverbank (Frome) near viaduct.