I think Sonchus asper (Prickly Sowthistle) on 26 May 2017 is also Sonchus asper and might cause confusion if someone is trying a comparison. (Now re-identified.)
I understand that Sonchus asper sometimes has red stems, maybe because of temperature, age, rate of growth, etc. HGW plants must have grown at the rate of knots as they appeared suddenly and grew so rapidly.